Cummins 6CT or 6CTA in 31B?
Moderators: CaptPatrick, mike ohlstein, Bruce
Cummins 6CT or 6CTA in 31B?
I’ve read of cat 3116 and 3208s in 31Bs, even Detroit 453s. Why not a 6CT300 or 6CTA350? 6CT300 with no aftercooler sounds awesome. The weight of the motors I think might help achieve the same head sea ride some people have mentioned with 3208’s and that motor at that power level ought to run forever. 6CT is smaller than a 3208 in all dimensions but height, where it is 1” taller from what I have seen. The thing I don’t know anything about is how do you make use of that torque with a small prop.
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
Yes 3208 Cats fit in the boats and pushed them very well and we're a standard 31 Bertram option. You said 4-53's yep they were a standard offering too. Capy has 6-53's in his boat and I think one of Whalers boats had the 6-53 twin turbo motors before he pulled them out..talk about screamers!
So yes those motors fit with a shoehorn, a sawzall and a supply of fiberglass supplies. Boxs needed to grow, deck cut back and bulkhead moved. And when I say they fit...it is they fit but maintence wasn't easy as motors took up substantial space.
Now comes my question...WHY?
Years ago those big motors are what was available in higher hp, so if faster diesel cruise is what you were after, those are the motors you installed. Today we have Yanmars, Perkins, Volvos and the Cummins all offering motors that have more power then our boats can handle in sizes and weights that can just slip in the engine compartment leaving ample room to maintain motors with room for a gen set.
Motors your talking about are a bit larger and would need a bit more finesse getting them to fit. Tons of torque so your changing struts, wheels, couplers, shaft logs and packing glands. Depending on how low you can get motors in boat you may be stuck spinning a smaller wheels or going with prop pockets to utilize the power...or let them run easy. But all that weight and displacement may be burning more fuel then a package sized to our boats. And that brings me back to WHY? Why go that route when better offerings are on the market.
Have an in on the motors? Just want to could be very good reasons...
So yes those motors fit with a shoehorn, a sawzall and a supply of fiberglass supplies. Boxs needed to grow, deck cut back and bulkhead moved. And when I say they fit...it is they fit but maintence wasn't easy as motors took up substantial space.
Now comes my question...WHY?
Years ago those big motors are what was available in higher hp, so if faster diesel cruise is what you were after, those are the motors you installed. Today we have Yanmars, Perkins, Volvos and the Cummins all offering motors that have more power then our boats can handle in sizes and weights that can just slip in the engine compartment leaving ample room to maintain motors with room for a gen set.
Motors your talking about are a bit larger and would need a bit more finesse getting them to fit. Tons of torque so your changing struts, wheels, couplers, shaft logs and packing glands. Depending on how low you can get motors in boat you may be stuck spinning a smaller wheels or going with prop pockets to utilize the power...or let them run easy. But all that weight and displacement may be burning more fuel then a package sized to our boats. And that brings me back to WHY? Why go that route when better offerings are on the market.
Have an in on the motors? Just want to could be very good reasons...
Re: Cummins 6CT or 6CTA in 31B?
Carl,
Just a hypothetical. The non aftercooled “ct300” model I would think would be easier to maintain than the CTA and id think would hardly be working to power a 31 Bahia Mar. I am looking at a total gut aft of the cabin bulkhead really (including beds, struts, shaft logs, rudders and deck- and no I’m not a sadist, I just love boats and building stuff) so I am just looking for opinions. One of the things I’m trying to read up on and I understand little is the difference between hp torque and prop size. I know there’s a mathematical relationship between hp and torque and rpm. Just trying to learn honestly. 99% sure I’ll reuse my older refreshed 6bta’s with new gears for now and if I have issues try to find newer recon’s or reman’s, but part of me is intrigued by the stated amazing head sea properties of the 31b’s powered with older bigger diesels.
Just a hypothetical. The non aftercooled “ct300” model I would think would be easier to maintain than the CTA and id think would hardly be working to power a 31 Bahia Mar. I am looking at a total gut aft of the cabin bulkhead really (including beds, struts, shaft logs, rudders and deck- and no I’m not a sadist, I just love boats and building stuff) so I am just looking for opinions. One of the things I’m trying to read up on and I understand little is the difference between hp torque and prop size. I know there’s a mathematical relationship between hp and torque and rpm. Just trying to learn honestly. 99% sure I’ll reuse my older refreshed 6bta’s with new gears for now and if I have issues try to find newer recon’s or reman’s, but part of me is intrigued by the stated amazing head sea properties of the 31b’s powered with older bigger diesels.
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
Devin,
There are a couple of free prop calculators on line that will offer a good ballpark prop size. See what they call for then work it backwards...strut height and angle to fit, where shaft comes in boat angle of trans and motor. Motor location.
I'd be pretty Leary running big props at tall angles unless you want to dig the boats nose into the seas. Then again run it easy with smaller prop and try to work it like Bob Lico does... it's a maybe...but it's an awful lot of work for a maybe in my boat.
Not to discourage you...just saying you have proven and not proven avenues to take. I like to push the envelope, but seen many theories die in real life. Then again it depends on who it coming up with the ideas...
There are a couple of free prop calculators on line that will offer a good ballpark prop size. See what they call for then work it backwards...strut height and angle to fit, where shaft comes in boat angle of trans and motor. Motor location.
I'd be pretty Leary running big props at tall angles unless you want to dig the boats nose into the seas. Then again run it easy with smaller prop and try to work it like Bob Lico does... it's a maybe...but it's an awful lot of work for a maybe in my boat.
Not to discourage you...just saying you have proven and not proven avenues to take. I like to push the envelope, but seen many theories die in real life. Then again it depends on who it coming up with the ideas...
Re: Cummins 6CT or 6CTA in 31B?
Crows Nest has DD 8.2s (big motors). She also had a swim platform, half tower with heavy electronics, 8D batteries, a Westerbeke genny, and a Murray Bros. big chair. She sat about 3" lower than she does now. Everything is out but the motors--she uses 2 group 31s for starting. Although the head sea ride was good, she's grab a chine and just lay on her side some times when she was heavy. It was a semi-awful experience until you got used to it. I took all that weight out of the boat and she rides great now--no grabbing a chine. Moral of the story--be wary of a lot of weight in a B31. Not always a good thing.
1968 B20 Moppie - Hull # 201-937
1969 B31 FBC - Hull # 315-881 (sold)
1977 B31 FBC - Hull # BERG1652M77J (sold)
1969 B31 FBC - Hull # 315-881 (sold)
1977 B31 FBC - Hull # BERG1652M77J (sold)
Re: Cummins 6CT or 6CTA in 31B?
John-
What is the weigh ton those motors? Thought they came in at 1100lbs which is about the same as the Cummins 6BT.
What is the weigh ton those motors? Thought they came in at 1100lbs which is about the same as the Cummins 6BT.
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Carl
I was told that the 270's I have weighed in at about the same as the 454's but I saved a few pounds with the ZF Transmissions. They are lighter than the Borg Warners.
But you could fool me because she sits lower in the water that she did with the gassers. But then again diesel is heavier and we must of added almost an inch of glass when we redid the strut pads.
I was told that the 270's I have weighed in at about the same as the 454's but I saved a few pounds with the ZF Transmissions. They are lighter than the Borg Warners.
But you could fool me because she sits lower in the water that she did with the gassers. But then again diesel is heavier and we must of added almost an inch of glass when we redid the strut pads.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
Ok, played around with the prop calculator https://www.vicprop.com/planing_size.php lowering the rpm raises the torque rating on the calculator and calls for a larger Diameter prop. I get that a lower rpm motor needs to push more water per rev. But when I changed the ratio to 1.25:1 the wheel size dropped. Is there a reason people choose to run the largest prop diameter possible with a higher gear transmission vs a smaller wheel and lower gear ratio. Below are pics of the calculator. The engines I have won’t idle well below 750 rpms so that may effect the choice of prop size some. I’d love to hear thoughts on which ratio and prop size is better and why if anybody has the energy to post it. Thanks!
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
The larger the wheel the more efficient they are due to less slippage....to a point.
Look on the old bulletin board, one of the main bullets is a chart from Capy, you can see the slippage of the smaller diameter wheels compared to running larger.
Also look and see what others have run in similar setups, don't go reinventing the wheel...so to say.
300+ hp per side has been done in diesel for these boats...read up and see the performance of each, how they achieved, how they put the power to the water and how the boats ran. You'll see Bob Lico's hp is lower with a much faster, more economical cruise they anybody else I have seen...no prop pockets and he runs safe and steady. Wrong setup in these boats and the nose comes down taking over the steering at higher speeds. I'll also add Bob really reconfigured the boat in so many ways to achieve what he has along with some trick wheels that are outside the norm form many prop shops.
Also look and see how some guys installed - I think it was Yanmars at 415hp- or something like that per side...installed prop pockets and just loaded bucks into their boats and came away not running all that impressive numbers in regards to speed. Efficiency wasn't too good and that is before taking into account the cost of the project. I guess for some cost is not a driving factor, nor is efficiency...but then just consider it cutting down the boats range.
I'd expect to at least see 20" wheels and more like 22"...but that is NOT a recommendation nor a suggestion...only an expectation based on familiarity.
If you say well that's the numbers I plugged in and what I got...well its a computer and software, garbage in produces garbage out.
Try running with 1-1/2:1 reduction.
Look on the old bulletin board, one of the main bullets is a chart from Capy, you can see the slippage of the smaller diameter wheels compared to running larger.
Also look and see what others have run in similar setups, don't go reinventing the wheel...so to say.
300+ hp per side has been done in diesel for these boats...read up and see the performance of each, how they achieved, how they put the power to the water and how the boats ran. You'll see Bob Lico's hp is lower with a much faster, more economical cruise they anybody else I have seen...no prop pockets and he runs safe and steady. Wrong setup in these boats and the nose comes down taking over the steering at higher speeds. I'll also add Bob really reconfigured the boat in so many ways to achieve what he has along with some trick wheels that are outside the norm form many prop shops.
Also look and see how some guys installed - I think it was Yanmars at 415hp- or something like that per side...installed prop pockets and just loaded bucks into their boats and came away not running all that impressive numbers in regards to speed. Efficiency wasn't too good and that is before taking into account the cost of the project. I guess for some cost is not a driving factor, nor is efficiency...but then just consider it cutting down the boats range.
I'd expect to at least see 20" wheels and more like 22"...but that is NOT a recommendation nor a suggestion...only an expectation based on familiarity.
If you say well that's the numbers I plugged in and what I got...well its a computer and software, garbage in produces garbage out.
Try running with 1-1/2:1 reduction.
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
The issue you have is that the biggest prop you can spin is 21 inches. Even that is pushing it but those that are using a 21 inch prop are not experiencing any prop wash burn. I pretty much followed the crowd, and when we repowered with the 270 cummins, we started out with 20x23 props with cup. Hit it on the nose. Turn 2650 RPM's and just shy of 30 knots with 4 blade props. Three blade would pick up the top end but drops the cruise a little.
If I went up to 21 inch props, I would probably need to remove some pitch, and basically get the same end result in RPM's and speed.
Try not to drive yourself too crazy. Follow the crowd.
Question for you, when you put your numbers in the calculator are you sure of your specs. The beam is 11'2" and a weight of 13000 lbs for a Bahia Mar seems high. The Water line is 27 ft. That is how much sits in the water, due to the rise at the bow, which is not in the water, the water line does go to 28 feet.
If I went up to 21 inch props, I would probably need to remove some pitch, and basically get the same end result in RPM's and speed.
Try not to drive yourself too crazy. Follow the crowd.
Question for you, when you put your numbers in the calculator are you sure of your specs. The beam is 11'2" and a weight of 13000 lbs for a Bahia Mar seems high. The Water line is 27 ft. That is how much sits in the water, due to the rise at the bow, which is not in the water, the water line does go to 28 feet.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
Carl and Tony,
Your points are well taken and appreciated. Plan is set the boat up for 1.5:1 and 315hp 6Bs. I talked with guys from a couple rebuilders and they asked why I was thinking about ditching my current motors, which made me rethink it. Both said motors could be rebuilt and some new parts bolted on for many years of reliable service. This is the route I’m going. Experimenting would be crazy expensive and much much more if I was wrong(likely). As far as the calculator specs, I used a lwl pulled off the interwebs and the weight I was throwing everything and the kitchen sink at the boat for worst case scenario. The calc I used asked for beam at waterline and I just assumed it was narrower near the chine than at the gunwale. On the prop size, it sure seems like 21” is my best bet but I’d be very open to suggestions. I’d like a well mannered boat around the dock and that worries me a little. Underpropping would be fine, I did not buy this boat to go fast but sure don’t mind it either. That’s way down the road, so I can research props til my eyes bleed until I have to buy a set. Thanks again for the words of wisdom.
Your points are well taken and appreciated. Plan is set the boat up for 1.5:1 and 315hp 6Bs. I talked with guys from a couple rebuilders and they asked why I was thinking about ditching my current motors, which made me rethink it. Both said motors could be rebuilt and some new parts bolted on for many years of reliable service. This is the route I’m going. Experimenting would be crazy expensive and much much more if I was wrong(likely). As far as the calculator specs, I used a lwl pulled off the interwebs and the weight I was throwing everything and the kitchen sink at the boat for worst case scenario. The calc I used asked for beam at waterline and I just assumed it was narrower near the chine than at the gunwale. On the prop size, it sure seems like 21” is my best bet but I’d be very open to suggestions. I’d like a well mannered boat around the dock and that worries me a little. Underpropping would be fine, I did not buy this boat to go fast but sure don’t mind it either. That’s way down the road, so I can research props til my eyes bleed until I have to buy a set. Thanks again for the words of wisdom.
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
With 315's your boat will be fast without pushing the motors hard.
What is fast? I'm basing that on running in average seas you will not be able to utilize the speed you have in reserve.
On flat days you'll get a thrill and pass lots of boats...but won't be running with the go fasts
...if your a "to the pins" guy all bets are off.
After doing a conversion I have to say the motors are the easy part as they are pretty much a fixed price. It's all the other stuff that you "think" you know that really racks up the bill and slows down the installation. The further you veer from the "standard install" the more unknowns and that cost in time and money.
I think resale also becomes a factor going outside the box. Lots of buyers want something they can compare to with known expectations. True an odd monkey can bite and it only takes one. But two boats being sold, one with Cummins 315 hp 6BT Cummins or Cummins 6CT's in and about the same hp...which sells first at the same price? You have to make the boat for you...but for me at least I need to try and make it desirable for others if the time comes to sell. Could be me moving up, a lateral slide to a newer 31 Bertram, I move inland, financial, health issues or I croak and my wife wants to sell it. Of course, after she takes a few fishing trips, rides to the beach.
I installed 210's...but the boat is setup with beefed-up stringers capped with Alum U-Channel and 1-1/2" shafts. Custom struts and logs can handle 22" props at an 11 degree angle. Oversize fule lines and Racors SO "IF" I ever got the bug to go faster I could pull the 210's and install 6Bts in a higher hp configuration. I built it for me and the next person with easy repower choices.
It's not wisdom we are offering. It is sharing the mistakes we have seen or learned the hard way.
Then again what I see as a mistake others may not. I think 400+hp Yanmars and prop pockets in a 31 is a mistake...the guys that put them in may just have wanted them in a 31 Bertram and had the available funds to do it without ever needing to recoup the cost. In that case, if it made him happy...it was not a mistake.
What is fast? I'm basing that on running in average seas you will not be able to utilize the speed you have in reserve.
On flat days you'll get a thrill and pass lots of boats...but won't be running with the go fasts
...if your a "to the pins" guy all bets are off.
After doing a conversion I have to say the motors are the easy part as they are pretty much a fixed price. It's all the other stuff that you "think" you know that really racks up the bill and slows down the installation. The further you veer from the "standard install" the more unknowns and that cost in time and money.
I think resale also becomes a factor going outside the box. Lots of buyers want something they can compare to with known expectations. True an odd monkey can bite and it only takes one. But two boats being sold, one with Cummins 315 hp 6BT Cummins or Cummins 6CT's in and about the same hp...which sells first at the same price? You have to make the boat for you...but for me at least I need to try and make it desirable for others if the time comes to sell. Could be me moving up, a lateral slide to a newer 31 Bertram, I move inland, financial, health issues or I croak and my wife wants to sell it. Of course, after she takes a few fishing trips, rides to the beach.
I installed 210's...but the boat is setup with beefed-up stringers capped with Alum U-Channel and 1-1/2" shafts. Custom struts and logs can handle 22" props at an 11 degree angle. Oversize fule lines and Racors SO "IF" I ever got the bug to go faster I could pull the 210's and install 6Bts in a higher hp configuration. I built it for me and the next person with easy repower choices.
It's not wisdom we are offering. It is sharing the mistakes we have seen or learned the hard way.
Then again what I see as a mistake others may not. I think 400+hp Yanmars and prop pockets in a 31 is a mistake...the guys that put them in may just have wanted them in a 31 Bertram and had the available funds to do it without ever needing to recoup the cost. In that case, if it made him happy...it was not a mistake.
Re: Cummins 6CT or 6CTA in 31B?
carl thanks for the atta boy but i should mention when i started building my boat i decided the boat will never be sold for two generations and i would be dust and so would my son.however my grandson would say thanks grandpa. moving right along one of the secrets is to hang off the transom at cruise with one hand under gunnel and watch how the water is coming off the end of the stern . water should be smooth with white lines were the strakes area 27 knots.and the thrust white water from props should be exactly symmetrical in width, shape.you will immediately notice if your pushing a "brick" under the boat like a old fashion non contoured transducer. mine is dead flush with keel line (no easy job) .forget calculators i have 15' of boat waterline at cruise and you need brute torque to get to 27 knots and while she on her inner strakes you can now use HP. up to 36 knots. which is the safe maximum speed for a 31 Bertram.
capt.bob lico
bero13010473
bero13010473
Re: Cummins 6CT or 6CTA in 31B?
I don't know what the 8.2s weigh. I thought that they were close to the 3208s, but don't really know. The point of my post that was a 31 can be too heavy. Crows Nest ran heavier into a head sea hen I got her, but when she grabbed a chine it was not pleasant. Taking a few hundred pounds out of her made a huge difference. I was counting on it. I wouldn't have wanted to own the boat if it continued to grab a chine. Now she rides like a 31 should. I run her at 2200 rpm which gets a little more than 23 knts. The motors are loafing. They'll spin up to 3150 plus and she'll be at 30 knts and climbing (but about done). I haven't run her over 2300 in years. I can't afford to stress those motors. They're old and hard to get parts for.Carl wrote:John-
What is the weigh ton those motors? Thought they came in at 1100lbs which is about the same as the Cummins 6BT.
I do think the Cummins 6btas--210/220 hp to 315/330 hp are great motors for the boat
1968 B20 Moppie - Hull # 201-937
1969 B31 FBC - Hull # 315-881 (sold)
1977 B31 FBC - Hull # BERG1652M77J (sold)
1969 B31 FBC - Hull # 315-881 (sold)
1977 B31 FBC - Hull # BERG1652M77J (sold)
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Since most of us are not tweeking the boat like Bob does, so other than Bob, remember it is a 30 foot boat. How many times are you going to run at full cruise or higher. I believe way back when JP said he made about 15 Canyon trips and averaged around 15 knots. Some days he could run 28 knots, others not so much. So you can put as much Horse power you want into her, if you don't change shaft angle etc, etc, etc, you are not going to be able to get the performance Bob gets. Plus in 6 foot seas, unless you use to race boats like Bob, I don't think you would want to run the Boat like Bob does.
I have never been out on Bob's boat but from what I have heard from those that have she handles beautifully, at all speeds in some bad water. But not everyone has the ability or wants to get the boat to that point.
I have never been out on Bob's boat but from what I have heard from those that have she handles beautifully, at all speeds in some bad water. But not everyone has the ability or wants to get the boat to that point.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
Thanks for talking me off the ledge fellas. I’m the type that can’t leave well enough alone. That being said, I’m using the motors I have (315s)
I would really like to move weight around and lower shaft angle, I don’t know if I’ll go to the lengths mr lico did but I guess I will see how achievable it is for me. I am going to try to use his efforts and results to guide me. Thanks for the input from all.
I would really like to move weight around and lower shaft angle, I don’t know if I’ll go to the lengths mr lico did but I guess I will see how achievable it is for me. I am going to try to use his efforts and results to guide me. Thanks for the input from all.
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
i found the key is being modest. our marina has a nice guy but always in the fish with deep pockets and a bit loud. so for the 50th time of teaching "lessons" this day eight boats go from the fire island inlet to a ww11 sunken tanker called Combra that has tuna all around it.about 70 miles one way trip . he has a 38' contender with triple 350hp yamaha outboards.his boat does about 60mph as well as the mako with triples ,well needless to say we start to go back together,wave height about 4' wind swept waves . we put her up and level out to 24 knots riding the crest . after a hour i checked radar and he 7 miles back and pissed as well as the other 6 CC. some lay back and can not get on plane in the waves.we docked the boat and the contender comes in about a half hour later and he fuming . WTF with that boat , what do you mean? we were driving with feet up on dashboard using hand held autopilot drinking a beer. i said we were at low cruise chilling he was frustrated and we just brush it off as the others came in beat to hell. this happen countless times but the best was the 45' cabo trying to catch up with 850hp manns ,i could not by a drink at the bar.
capt.bob lico
bero13010473
bero13010473
- PeterPalmieri
- Senior Member
- Posts: 2612
- Joined: Nov 12th, '10, 11:26
- Location: Babylon, NY
Re: Cummins 6CT or 6CTA in 31B?
Bob, these stories never get old. My boat isn’t high tech or reimagined; a 50 year old boat with 454s. We run down the beach and it inevitably kicks up in the afternoon. We ride back my parents in their 80s sitting out on deck chairs and my grade school children playing cards in the cabin. Meanwhile grown men in half a million dollar boats, wearing bibs and holding on like it’s a rodeo watch me eventually catch up and pass them. There is nothing more fun then dropping the pins as you hit the following sea of FI Inlet.
There is no doubt getting out at 5am in glass calm seas their lines are in the water first and I occasionally long to cast a popper from the bow at fish breaking the water. But there is nothing better then getting home safe and not beating the heck out of your crew.
There is no doubt getting out at 5am in glass calm seas their lines are in the water first and I occasionally long to cast a popper from the bow at fish breaking the water. But there is nothing better then getting home safe and not beating the heck out of your crew.
1969 31 Bertram FBC "East Wind" hull #315939
Re: Cummins 6CT or 6CTA in 31B?
most are brainwashed into believing what they read in magazines and the salesman who sold him the boat. they take a customer (idid it as a captain with salesperson with me) out in the bay and the salesperson gives me the nod and i drop the hammer on triple 350 hp Yamaha's and we are doing 55 or 60mph as i told you a thousand times a totally mealiness number !!!!!! you cannot take a fishing cc at 60 in the ocean even on glass days because on the ninth gentle roller the boat will go into a flight like a ski jump and will come crashing down.you will wear that steering wheel TRUST ME. the atlantic ocean is a monster ready to swollen up the unsuspected big shot triple outboard CC ,28 knots is maximum cruise maybe 30 but fuel economy will drop.
capt.bob lico
bero13010473
bero13010473
Re: Cummins 6CT or 6CTA in 31B?
My father and his buddy have a 34’ pursuit center console in Islamorada and while it is a nice boat you cannot run in any kind of crap. It’s only good in well spaced rollers or maybe 2’ seas? Anything over which is very often it is a miserable slog and can’t keep it in a slow plane. It either wants to pop up and do 30 or dig a hole at 15. Not fun unless almost glass calm. Now a buddy had a 35’ predator (egg harbor bought the mold) with twin diesels and that boat would eat the seas up. No slowing down, just roll down the curtains and part the seas. I will be totally happy with 25 knots if I can get it. Sounds like 315hp Cummins can do that easily if I don’t screw anything up too badly.
Peter, my first offshore trip was on a 31B with 454’s called Vamos out of Port A, TX. It was freakin awesome and totally responsible for me getting my boat. I didn’t wind up with a FB model but I think I’ll be happier since I have little ones that can be on the same level with me.
Peter, my first offshore trip was on a 31B with 454’s called Vamos out of Port A, TX. It was freakin awesome and totally responsible for me getting my boat. I didn’t wind up with a FB model but I think I’ll be happier since I have little ones that can be on the same level with me.
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
Reading through various threads over the years, it seems that for a given motor setup, the 31 is faster than the 28.
Going through the original specs, with gassers and dry, the 31 is advertised to be by 1500# lighter. It is also longer, which helps.
Anyway, my point is that, if I can cruise my 28 at 24-25 knots effortlessly with my 240 Yanmars, then why would a 31 need more horsepower to achieve same speed?
There are a few 31’s here with same Yanmars that are faster and more eco than my 28.
I can achieve the rated 3300-3350 revs at wot, loaded, which suggests that my props are more or less the right ones.
If, as Bob says, you can’t go over 28 knots in the ocean or you’ll fly, then anything above that (240hp) is more or less useless.
Unless there are other, additional considerations to prefer a higher hp, that I’m not aware of.
For the record, I cruise @ 3000rpm @ 24-25 knots, @ 60-65 liters per hour. The european 4lha stp’s are rated at 10 hp more.
I used to cruise @2700, 2800, 2900 for extended periods in the past, thinking I shouldn't push the engines, but other than a lower speed, the economy was not better at all!
Going through the original specs, with gassers and dry, the 31 is advertised to be by 1500# lighter. It is also longer, which helps.
Anyway, my point is that, if I can cruise my 28 at 24-25 knots effortlessly with my 240 Yanmars, then why would a 31 need more horsepower to achieve same speed?
There are a few 31’s here with same Yanmars that are faster and more eco than my 28.
I can achieve the rated 3300-3350 revs at wot, loaded, which suggests that my props are more or less the right ones.
If, as Bob says, you can’t go over 28 knots in the ocean or you’ll fly, then anything above that (240hp) is more or less useless.
Unless there are other, additional considerations to prefer a higher hp, that I’m not aware of.
For the record, I cruise @ 3000rpm @ 24-25 knots, @ 60-65 liters per hour. The european 4lha stp’s are rated at 10 hp more.
I used to cruise @2700, 2800, 2900 for extended periods in the past, thinking I shouldn't push the engines, but other than a lower speed, the economy was not better at all!
1973 B28 FBC/2007 4LHA STP's - "Phantom Duck" - Hull "BER 00794 1172"
Re: Cummins 6CT or 6CTA in 31B?
Not speaking specifically to any Bertram experience, but on the days that you can it sure is nice to be able to pin it and scoot. For me personally, the boat I bought came with 2 6bta 315/330 engines and mg5050a 1.5:1 gears that the previous owner had gotten out of a 31 Tiara and planned to swap but never did. I think looking at all the experiences here, I would be happiest with 250-270hp, but I’ve got these and I’m going to see if I can use the power or not. If not, is it practical to derate the engines by under propping the motors and getting as much efficiency as possible?
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
Yannis I am going to say "because it all depends".
Load up a 31 with fuel, food, fishing gear, a few guys, maybe a tower, hardtop or enclosure a couple of guys, lots of ice for the fish and some extra push can be needed if the boat is still to travel at rated WOT.
Some people need to be faster, its why we have 4 door, mid size production cars with 707hp. Use it or not, it's there.
Practical and boats do not belong in the same sentence.
...and just because Bob says 28 is max does not mean 28 is max, plus I believe he was talking about CC with triple outboards.
And for the record, you have some great cruise numbers.
Load up a 31 with fuel, food, fishing gear, a few guys, maybe a tower, hardtop or enclosure a couple of guys, lots of ice for the fish and some extra push can be needed if the boat is still to travel at rated WOT.
Some people need to be faster, its why we have 4 door, mid size production cars with 707hp. Use it or not, it's there.
Practical and boats do not belong in the same sentence.
...and just because Bob says 28 is max does not mean 28 is max, plus I believe he was talking about CC with triple outboards.
And for the record, you have some great cruise numbers.
Re: Cummins 6CT or 6CTA in 31B?
Carl,
It’s always a pleasure when you bring me back on the straight line!
The 210’s might be slower on the 28 though. Before I bought my boat I was looking at another 28 with 210 volvos. I remember that boat’s cruising speed was in the 19-20 knot range. I understand you do more than that.
It’s always a pleasure when you bring me back on the straight line!
The 210’s might be slower on the 28 though. Before I bought my boat I was looking at another 28 with 210 volvos. I remember that boat’s cruising speed was in the 19-20 knot range. I understand you do more than that.
1973 B28 FBC/2007 4LHA STP's - "Phantom Duck" - Hull "BER 00794 1172"
Re: Cummins 6CT or 6CTA in 31B?
Yannis wrote:Carl,
It’s always a pleasure when you bring me back on the straight line!
The 210’s might be slower on the 28 though. Before I bought my boat I was looking at another 28 with 210 volvos. I remember that boat’s cruising speed was in the 19-20 knot range. I understand you do more than that.
The Cummins 210's are heavy and big for a 28 in my opinion. Now the Cummins 4BT's with aftercooler at 250hp would make your boat a screamer. They'd be alot quicker in my boat too.
My goal is a solid 20knot cruise at 2200 and have motors hit 2650. Now I need to push them up to my high cruise of 2300 to hit 20 knots...I still have kinks to work out but I am optimistic I can get there. Till then I'm happy chugging around at 2100 letting them run nice and easy. No disillusions here, I am in my expected range.
Re: Cummins 6CT or 6CTA in 31B?
The 210’s might be slower on the 28 though. Before I bought my boat I was looking at another 28 with 210 volvos. I remember that boat’s cruising speed was in the 19-20 knot range. I understand you do more than that.[/quote]
The Cummins 210's are heavy and big for a 28 in my opinion. Now the Cummins 4BT's with aftercooler at 250hp would make your boat a screamer. They'd be alot quicker in my boat too.
My goal is a solid 20knot cruise at 2200 and have motors hit 2650. Now I need to push them up to my high cruise of 2300 to hit 20 knots...I still have kinks to work out but I am optimistic I can get there. Till then I'm happy chugging around at 2100 letting them run nice and easy. No disillusions here, I am in my expected range.[/quote]
Carl, what tweaks do you intend to achieve your desired cruise?
The Cummins 210's are heavy and big for a 28 in my opinion. Now the Cummins 4BT's with aftercooler at 250hp would make your boat a screamer. They'd be alot quicker in my boat too.
My goal is a solid 20knot cruise at 2200 and have motors hit 2650. Now I need to push them up to my high cruise of 2300 to hit 20 knots...I still have kinks to work out but I am optimistic I can get there. Till then I'm happy chugging around at 2100 letting them run nice and easy. No disillusions here, I am in my expected range.[/quote]
Carl, what tweaks do you intend to achieve your desired cruise?
Devin
31 Bahia Mar
31 Bahia Mar
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Yannis
I don't believe the 6 cylinder 210's will fit into the 28. The 4 cylinder Cummins should squeeze in there. I believe the knock on the 4 cylinder Cummins was that they shake a lot at idle.
Devin
The 315/330 Cummins are pretty common in the 31. Same block as the 250/270. You will be fine with them. You will cruise around 28 knots. I am around 24 with the 270's and that is at 2300 RPM's.
When I repowered I was looking at the 315 Yanmars or the 315/330 Cummins. Walked away from the Yanmar due to cost difference. When it came down to the Cummins, settled on the 270's because it had a fresh water cooled after cooler so less to worry about for servicing. Given the size of our boats, I would say for the most part 25 knots is the sweet spot depending on how you use the boat. If you go offshore a lot, I guarantee you will find that the 31 with 270 Cummins vs one with the 315/330 will be averaging the same speed due to sea conditions setting the limit.
Now I will admit, after trolling around for 8 hours, it is nice to be able to crank it up coming home on a flat ocean.
I don't believe the 6 cylinder 210's will fit into the 28. The 4 cylinder Cummins should squeeze in there. I believe the knock on the 4 cylinder Cummins was that they shake a lot at idle.
Devin
The 315/330 Cummins are pretty common in the 31. Same block as the 250/270. You will be fine with them. You will cruise around 28 knots. I am around 24 with the 270's and that is at 2300 RPM's.
When I repowered I was looking at the 315 Yanmars or the 315/330 Cummins. Walked away from the Yanmar due to cost difference. When it came down to the Cummins, settled on the 270's because it had a fresh water cooled after cooler so less to worry about for servicing. Given the size of our boats, I would say for the most part 25 knots is the sweet spot depending on how you use the boat. If you go offshore a lot, I guarantee you will find that the 31 with 270 Cummins vs one with the 315/330 will be averaging the same speed due to sea conditions setting the limit.
Now I will admit, after trolling around for 8 hours, it is nice to be able to crank it up coming home on a flat ocean.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
devinfox wrote: Carl, what tweaks do you intend to achieve your desired cruise?
Tweak #1 is to modify the exhaust.
I set it up the way I did to verify motors ran ok as they were RTO's, it was the quickest and easiest way. I hoped it would have been fine, but knew I was pushing it a bit. So the modification may initially be to pull off/divert some of the cooling water to the showerhead, giving less volume, less steam and that reduction of volume in the exhaust system should reduce back pressure while still cooling the exhaust enough. Not my trick but something from Tony Athens of Seaboard Marine. If I reduce backpressure I could push up the throttles more when I want to cruise at 2300. Right now I stay under 2200 keeping backpressure under 1-1/2 psi. Long term is to go with a dry riser of the right diameter which will reduce backpressure and "may" allow motor to breathe a little easier...maybe get a couple more RPM to tack onto the WOT. What am I looking for in RPM...I'll take 5 or 10, more would be great, but doubt that is a reality. The big reason is to get motors to run easier with less heat in the heads.
Tweak #2 is get away from the 4 blade wheel.
Going from 4 blade to a 3 blade wheel should bump up my RPM by 200. 200 rpm could go into an inch of pitch OR cup or split it for a little pitch and some rpm to bring the 2600 to 2650. An inch of pitch "should" translate into 1 knot faster at same rpm.
Or I go 3 blade and instead of staying with 20 x 20 I go 21 x 19...the larger wheel "should" be more efficient, but have not formula or rule of thumb to go by. So I wait and see what used wheels com up for sale and I'll give a try.
I am really close so it should only be small tweaks to give small results...but that is all I am looking for.
Re: Cummins 6CT or 6CTA in 31B?
Carl you have all the photos and details of my exhaust with 00000000 back pressure and lifetime trick sprinkler--------use it!
capt.bob lico
bero13010473
bero13010473
Re: Cummins 6CT or 6CTA in 31B?
bob lico wrote:Carl you have all the photos and details of my exhaust with 00000000 back pressure and lifetime trick sprinkler--------use it!
My Summer project is to use the boat, enjoy the boat, start some fix'en up and bringing back in shape and take care of maintenance.
My Fall project is to catch a nice Bass.
My Winter project is Helm Windows and Exhaust.
Re: Cummins 6CT or 6CTA in 31B?
Bob, I’ve searched and searched for pics of your exhaust and engine beds, mounts etc. I want to copy your engine placement (fore/aft) and prop shaft angles if I can. I have seen your exhaust elbow /outboard stringer exhaust pics but can’t find any of how you got your motors so low and close to the hull. Do you have any you could share or a link to where I could them?
Devin
31 Bahia Mar
31 Bahia Mar
Re: Cummins 6CT or 6CTA in 31B?
devinfox wrote: can’t find any of how you got your motors so low and close to the hull.
You can make a motor/trans template and OR shorten and cap the stringers and drop motor in place, shim as required then make your mounts to fit.
Re: Cummins 6CT or 6CTA in 31B?
i have posted at least 20 times differant angles of the engine and exhaust and engine placement as well as photos of shaft log patrusion and carl has every bit of it loged however the site "THE BERTRAM SOCIETY" also has photos of shaft log placement, engine cool air intake, exhaust configuration. they could not understand no surge tubes and how i back up wot. and make every attempt to hydraulic the engines to no avail (i could get engines at the time) the room along side the engine are precious for generator and black water tank to put surge tubes is absurd.
capt.bob lico
bero13010473
bero13010473
Re: Cummins 6CT or 6CTA in 31B?
Bob, I found lots of posts but had old links to pics I think. Has been a little while since I last looked, I spent a sleepless night trying to comb through all your posts searching just your name as an advanced search query. Lots of good stuff though. Carl, that’s an excellent descriptions, my brain grasped that immediately, thank you.
Devin
31 Bahia Mar
31 Bahia Mar
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
bob lico wrote:i have posted at least 20 times differant angles of the engine and exhaust and engine placement as well as photos of shaft log patrusion and carl has every bit of it loged however the site "THE BERTRAM SOCIETY" also has photos of shaft log placement, engine cool air intake, exhaust configuration. they could not understand no surge tubes and how i back up wot. and make every attempt to hydraulic the engines to no avail (i could get engines at the time) the room along side the engine are precious for generator and black water tank to put surge tubes is absurd.
Bob
Not sure but it seems for some of us the old posts have disappeared. I for one can not search for anything on this board anymore. All I get post does not exist.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
Tony i was not aware of this . your saying 16 years of posting has disappear !!!!!!
capt.bob lico
bero13010473
bero13010473
Re: Cummins 6CT or 6CTA in 31B?
Devin
31 Bahia Mar
31 Bahia Mar
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Bobbob lico wrote:Tony i was not aware of this . your saying 16 years of posting has disappear !!!!!!
It has for me.
1975 FBC BERG1467-315
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Devin
Never heastdc of thar brefore. Interesting.
Never heastdc of thar brefore. Interesting.
1975 FBC BERG1467-315
- mike ohlstein
- Site Admin
- Posts: 2394
- Joined: Jun 29th, '06, 11:39
- Location: So many things seem like no-brainers until you run into someone with no brain.
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Tony Meola wrote:Tony i was not aware of this . your saying 16 years of posting has disappear !!!!!!
Bob
It has for me.
Nothing has been deleted from this site. If you think that something is missing, please let me know.
Re: Cummins 6CT or 6CTA in 31B?
I don't know how difficult "opening up the vault" would be, but it'd be kinda fun to go back 20 years and read the old posts from the likes of "Hell Diver" Stan, the "Prince of Potions" Judge etc.Nothing has been deleted from this site. If you think that something is missing, please let me know.
And UV's short story(s?)...
Re: Cummins 6CT or 6CTA in 31B?
The old stuff is on the old board
http://bertram31.com/
search or look back from here
http://www.bertram31.com/bb/bbs.cgi?noframes
http://bertram31.com/
search or look back from here
http://www.bertram31.com/bb/bbs.cgi?noframes
Re: Cummins 6CT or 6CTA in 31B?
The opposed piston motor has been out a good long time with lots of advantages. Wanna see a cool motor check out the Napier Deltic opposed piston motors.
https://en.wikipedia.org/wiki/Napier_Deltic
Invent or remaster
- mike ohlstein
- Site Admin
- Posts: 2394
- Joined: Jun 29th, '06, 11:39
- Location: So many things seem like no-brainers until you run into someone with no brain.
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Too bad this guy passed in Feb. 2019. It seems that his dreams may have died with him. His website hasn't been updated since late 2018.
Re: Cummins 6CT or 6CTA in 31B?
Tony,
Did a quick search for bob lico and over 10 pages came up. Not sure where your having trouble.
Now when it comes to pics, people's hosting sites over the years have changed and may not be showing.
Nothing was ever deleted unless it was by the poster themselves. Pat did have a web failure way back when the current board came online but he lost very little.
The old board is still viable as a search function.
Did a quick search for bob lico and over 10 pages came up. Not sure where your having trouble.
Now when it comes to pics, people's hosting sites over the years have changed and may not be showing.
Nothing was ever deleted unless it was by the poster themselves. Pat did have a web failure way back when the current board came online but he lost very little.
The old board is still viable as a search function.
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
When I use the search function in the upper right I usually draw blanks.
But if I understand you correctly, I just need to go over to the old board. I will take alook and let you know how I make out.
But if I understand you correctly, I just need to go over to the old board. I will take alook and let you know how I make out.
1975 FBC BERG1467-315
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Bruce
Desk Top, smart phone or note pad I get the same results. I can see a thread, but if I try to open it i get a message telling me there is no content.
Doesn't matter if I am on my internet at home or someone else's.
I will try again later on today. I will disable my anti virus to see what happens. Maybe that is my issue.
Desk Top, smart phone or note pad I get the same results. I can see a thread, but if I try to open it i get a message telling me there is no content.
Doesn't matter if I am on my internet at home or someone else's.
I will try again later on today. I will disable my anti virus to see what happens. Maybe that is my issue.
1975 FBC BERG1467-315
- mike ohlstein
- Site Admin
- Posts: 2394
- Joined: Jun 29th, '06, 11:39
- Location: So many things seem like no-brainers until you run into someone with no brain.
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Post a link to the dead thread
-
- Senior Member
- Posts: 7036
- Joined: Jun 29th, '06, 21:24
- Location: Hillsdale, New Jersey
- Contact:
Re: Cummins 6CT or 6CTA in 31B?
Mike
The thread will not open for me do I can't post the link.
Lets say I do a search for helm chair. Ii will show a page of posts, some as of today others going back further. If I try to jump to a post older than 2019 i get a blank page and at the top it says that the post does not exist.
I tried opening 2018 posts, 2015 posts I am coming up empty.
I turned off my anti virus still doesn't work.
I assumed it was my system. I still think it might be since others don't seem to have this problem. It is just that I haved 3 different devices that have the same issue. Doesn't seem to happen on other boards.
Sorry I have nothing else for you on this.
The thread will not open for me do I can't post the link.
Lets say I do a search for helm chair. Ii will show a page of posts, some as of today others going back further. If I try to jump to a post older than 2019 i get a blank page and at the top it says that the post does not exist.
I tried opening 2018 posts, 2015 posts I am coming up empty.
I turned off my anti virus still doesn't work.
I assumed it was my system. I still think it might be since others don't seem to have this problem. It is just that I haved 3 different devices that have the same issue. Doesn't seem to happen on other boards.
Sorry I have nothing else for you on this.
1975 FBC BERG1467-315
Re: Cummins 6CT or 6CTA in 31B?
Tony-
If I do a search on helm chairs I go back to 2006 with posts.
Have you cleared your cache recently?
...and once in awhile I like to delete the cookies from this site.
Bottom of this page in blue bar...give a click on delete cookies, then click accept.
If I do a search on helm chairs I go back to 2006 with posts.
Have you cleared your cache recently?
...and once in awhile I like to delete the cookies from this site.
Bottom of this page in blue bar...give a click on delete cookies, then click accept.
Who is online
Users browsing this forum: No registered users and 191 guests