cummins 370

1962 31 · Post by **1962 31** » Jul 21st, '20, 09:05

anyone run the 370 cummins
was wondering what kind of numbers cruise and fuel burn
i picked up a set to rebuild not sure if im going to drop them in mine and sell my 201s or sell the 370s

Tony Meola · Post by **Tony Meola** » Jul 21st, '20, 21:27

Tom

I think Jimmy G has them in Killer Instinct. I know the shop that installed them. I know they had to de tune them at idle to keep the idle speed down. I believe Jimmy is close to 40 knots at the top end. As far as GPH, I am not sure. But I do not think it is too bad. Would be a little more than you burn with the 210's. Plus you might need 1 3/4 shafts.

He has not posted in a while, but try sending him a PM.

CHolgerson · Post by **CHolgerson** » Jul 22nd, '20, 07:21

I would think you could cruise close to 30 knots but you would need trolling valves to make the boat manageable around the dock. My Dad has 300 hp cummins without trolling valves and it is a handful around the marina. He can cruise 26 knots.

CHolgerson · Post by **CHolgerson** » Jul 22nd, '20, 07:24

If you do decide to sell the 370s please let me know. I am an interested buyer.

Best Regards
Chris

bob lico · Post by **bob lico** » Jul 22nd, '20, 08:59

tony, Jimmy G has QSB-380hp install by john lane in Tom`s river NJ. 370hp 6bta-m3 are a thousands times better then the older 300hp 6BTA- 970 CPL which should be treated as a 250 hp due to multiple inherited problems that were corrected in 1994 to 2005.the 370hp 6BTA-m3 (storm block) starting in 2004 with give you same fuel economy AS the old 210 AT THE SAME SPEED! however when you drop the hammer from 21-22 knots and cruise at 26 the fuel economy will drop somewhat.the bottom of a 31 Bertram is very interesting ,when you exceed 24 knots the boat starts to rise up on lifting strakes dramatically decreasing surface friction so fuel economy does not go up proportional to HP. increase.

Mark · Post by **Mark** » Jul 22nd, '20, 11:47

Tom,

Went out with a guy to the Hudson who has the 370s but they were in a 34 Pursuit. Bigger boat so probably not a good comparison. Ran about 80 out running 20-22 knots, trolled about 60 miles, then ran about 75 back at 22-23. Burned about 250.

Mark

PeterPalmieri · Post by **PeterPalmieri** » Jul 22nd, '20, 18:49

If you install the 370s I would be interested in your 210s, keep me in mind.

Tony Meola · Post by **Tony Meola** » Jul 22nd, '20, 20:16

Bob

To help Tom out, do you know of any in a 31with the 370's and what the performance is. I would still think the top end is going to be in the upper 30 knot range, with a fuel burn between 18 to 20 Gallons an hour. But he should have a cruise close to 30 knots at that rate. Granted that speed will be far and few between I would think he would be running between 25 to 28 knots unless he has an absolute dead flat ocean with a fuel burn between 15 to 18 gallons an hour. But that is just me guessing.

Bruce · Post by **Bruce** » Jul 23rd, '20, 11:01

One of the 31's I did was 370. Don't remember fuel burn, but top end was 36 knots. Biggest issue was putting the power to the wheels and loading the engines with the limited prop diameter without pockets. Prop tweaking is a must.

I also did a set of QSB but cut the hull for pockets to swing a bigger prop to get top end without a fast idle or trolling valves.

Carl · Post by **Carl** » Jul 23rd, '20, 13:18

Bruce wrote: Biggest issue was putting the power to the wheels and loading the engines with the limited prop diameter without pockets. Prop tweaking is a must.

Bruce- I may have asked this question before, but I still don't quite get it. Why can't motors be run as lesser loads provided you do not over-rev them...turn in the WOT screw.
Within reason...can't have motors just freewheeling for hours either. That I doubt would be good.

Or is it trying to get whatever speed you can get out of them to make owner happy.

bob lico · Post by **bob lico** » Jul 23rd, '20, 18:27

maybe it's my vocabulary i am not getting thru. 370 hp cummins RUN THE SON OF A BITCH WITH THE THROTTLES BACK OFF!!!!!!!! to 2200rpm not 30 knot cruise a real 27 knot cruise with extremely perfected props with the same fuel economy as 210 KEEPING IN MIND YOU ARE DOING 27 KNOTS, NOT FUEL BURN, HOW MANY MILES DID YOU GO COMPARE TO THE Bertram doing 21 knots with 210 hp with same fuel burn.never,never exceed 34 knots with those 370 hp cummins pull it out of water remove props and remove pitch!!!!

CHolgerson · Post by **CHolgerson** » Jul 23rd, '20, 20:38

Bob,
What type of prop would be required to run 27 knots at 2200 rpm and still have a dockable boat?

Carl · Post by **Carl** » Jul 24th, '20, 06:24

CHolgerson wrote:Bob,
What type of prop would be required to run 27 knots at 2200 rpm and still have a dockable boat?

What is considered a dockable boat is in the eye of the docker.

I do not like speaking for others...but has that ever stopped me?? Sometimes....

Anyway I believe Bobs idea of ideal is to decrease the pitch of the wheel for slower speed at idle and slower speed maneuvering...then a kind of artificial pitch for a quicker cruise is done by adding extensive cup and rake.

bob lico wrote:maybe it's my vocabulary i am not getting thru.

I'm not sure who you're directing that to, but my question to Bruce...or anyone still remains, is it important to significantly load the motors. If so why?

Let me rephrase my question-

Tom is now the perfect example.

Running 20 x 22 wheels with 210's, he pulls those motors and installs 370's.
For argument sake, let's say Tom is already setup with 1-3/4" shafts to handle the additional torque.

IF Tom was to run the same 20 x 22 wheels the motors would not be highly loaded...would running the 370's like that hurt the motors?

bob lico · Post by **bob lico** » Jul 24th, '20, 19:06

370hp cummins in a 31 Bertram with proper balance (travel lift with one strap directly under main bulkhead or bahia mar 6" in front of engine box.like a seesaw boat goes down at transom. ok propeller 3 blade,21" dia,231/2" pitch on FBC and 24" on Bahia Mar NEXT and the most important you are not the least bit concern what the Prop. people recommend you want the entire prop. cupped from hub all the way around tip to back side. assuming you have already gone to larger rudders you can travel in a marina area at 5 knots on one engine and use both engines to dock ,very easy. you will run 27 knots cruise at 2300rpm and have proper load on engine and torque curve starts at 2000 rpm. with the proper set up you will definitely beat the TOTAL fuel economy of 210 hp cummins. i did not ask you to rake props because prop builder will give you a song and dance so you may use small trim tabs in 5 to 6' head seas.the boat will do 33 to 34 knots wot. but that's a nonsense number you will never utilize or maybe for two minutes.

Tony Meola · Post by **Tony Meola** » Jul 24th, '20, 20:36

Bob

Ok I understand that. Thank You.

CHolgerson · Post by **CHolgerson** » Jul 25th, '20, 08:07

Bob,
Thank you for that information. You certainly answered my question. I hope all is well.

Chris

bob lico · Post by **bob lico** » Jul 25th, '20, 08:27

all is not well but at least on August 12 you can see your love ones in a nursing home with outside visitation weather permitting.she is paralize on left side from stroke.

PeterPalmieri · Post by **PeterPalmieri** » Jul 25th, '20, 12:39

Bob I can only assume you are talking about your beautiful wife. So sorry to hear.

CHolgerson · Post by **CHolgerson** » Jul 25th, '20, 16:38

Bob,

My prayers go out to you and your family.

Best Regards,
Chris

bob lico · Post by **bob lico** » Jul 25th, '20, 18:15

yes peter my loving wife of 53 years that i took to my senior prom in high school.

Tony Meola · Post by **Tony Meola** » Jul 25th, '20, 20:53

Bob

Sorry to hear about your wife. Our prayers are with you.

jap201 · Post by **jap201** » Jul 26th, '20, 05:57

Not the same boat, but I had a 32 blackfin with 330 cummins for 10 years. it had a tower and riggers, chair, 300gal fuel so lots of weight. it was heavier than the b31, but both deep v's. think i was swinging 24x24 or 25x25 wheels, don't remember for sure about the wheel size, been awhile. idled at 5-6kts, cruised 2200-2300 at 22-24kts and 1.1nmpg. engines really wanted to run at 2500 rpm, but that got me at 25 kts, and i was never in that much of a rush. boat topped close to 30kts. only needed trolling valves trolling for giants. excellent engines. 370's in a 31 will really get up and go. like bob said, i'll bet you'd see 33+kts wot.

Bruce · Post by **Bruce** » Jul 26th, '20, 08:12

Carl,
No problem with what you or Bob said.

My issue as an engine installer was to get the max output of an engine up to its rated power for the application.
Having a little extra is good. But when you can only use 75% of rated power because you can't load them enough, one is wasting weight and power.

It's the reason why I turned down 2 31 repowers that the owners wanted to use the Yanmar 440hp engines.

I got the first set of QSB's when they came out in Florida. Sitting down with slide rule and prop guy I figured out what it would take to load engines without a 10 knot idle or trolling valves.
Swinging a larger prop would take pockets without changing shaft angle and possibly leading to a plowing situation which I had been on two 31's that I surveyed with repowers where shaft angle was changed to fit a larger diameter prop. Dangerous to say the least.

Bob has figured out prop tweaking for the Cummins. Something I didn't have in the early days of 31 diesel repowers. Props have come a long way since then.

1962 31 · Post by **1962 31** » Jul 26th, '20, 10:44

First and foremost prayers for your wife and family Bob

I picked up the motors yesterday morning 12 hour round trip to finger lakes
They were underwater and I knew that before hand
They must of went front down and only got water in the blocks
turbos clean and turn freely
Only surface rust under valve covers not a chunky mess
Gears look clean from what I can see
The motors bar over smoothly
I'm tired and taking the kids on the skiff today
I'll unload em from the truck tomorrow and get deeper into em thanks for all the info so far guys

bob lico · Post by **bob lico** » Jul 26th, '20, 13:03

bruce the funny thing is the raw propellers come from your neck of the woods. St Augustine FL. (Ron Ellis) props. you essentially have a three bladed propeller with just about the same amount of metal in the blade area as a four blade.Just accept it i am not going to write a book on how this is done.secondly the boat runs in a perfect slightly bow proud angle from 21 knots on up to hyperspace speed if you want to. is there a drawback----YES the first 10' of the boat never touches the water with 370 or 330hp SO the barnacles that cling to the bow area when the boat is in her slip never get wash off as a 31 Bertram that plows water.when you are piloting your 370hp cummins power 31 and you you enter a 5mph Zone you just use one engine and with single lever controls you play touch and go you can also glide in tight areas by just touching either throttle than back into slip with touch and go to keep her straight NEVER,NEVER use steering wheel use rudder indicator to keep the steering wheel at zero and never touch it again.the 370hp cummins must be installed as low and as far back so turbo oil feed is touching the engine box and you can get your pinky finger tightly under rear of gears.fuel ,batteries, fresh water, dead center of keel.the key is perfect balance or all the hard work is negated.

Carl · Post by **Carl** » Jul 26th, '20, 18:12

53 years is quite the statement.

I had not realized your wife was not at home but in a nursing home. It is never a good nor easy time having to deal with what you, your wife and your family are going through...but in this mess with COVID restrictions it's a whole new level. My prayers NY stays on course with good numbers so you get to spend some time together again.

Carl · Post by **Carl** » Jul 26th, '20, 18:26

Thank you Bruce...I was afraid that not pushing the motors enough would or could create issues like the ones created by prolonged idling. Obviously not an issue for me with my motors...but someday in my dreams I'd like a boat that could cruise faster then I want to go. Even though I could afford to fix them if I pushed them too hard, I'd rather not have I'd like to keep that dream intact.

bob lico · Post by **bob lico** » Jul 26th, '20, 18:32

i kneel in the dirt outside her window every day as they bring her wheelchair to the window.she can only move her right hand but recently just started crying when i brought her grand daughter in high school cap an gown after HS graduation . trust me the war was a lot easier!!!!!!

DanielM · Post by **DanielM** » Jul 26th, '20, 19:41

Bob, my thoughts and prayers are with you, your wife and family.

John F. · Post by **John F.** » Jul 26th, '20, 21:44

Bob

I'm sorry to hear about your wife. You and yours are in our thoughts. Take care

John

JH_B28 · Post by **JH_B28** » Jul 27th, '20, 09:21

Ours had the 370's, cruise at 2400 was in the 25-26 kt range, WOT was 34kts. On flat days we would do 2600 touching 30kts. We never precisely measured fuel economy but with rough calculations we were doing 15-16gph at cruise. We ran Michigan DJX 21x24 med cup 3 blades.
They are great engines and its nice to have that extra power but as Bruce said, the challenge is loading the engines correctly and putting the power to the wheels, given the limited space. If I would do it all over again, I would go with the 330's. You can achieve nearly the same numbers.

Regards,

1962 31 · Post by **1962 31** » Jul 27th, '20, 14:15

CPL2280
I JUST POPPED A HEAD OFF 1 OF THE MOTORS NOT EVEN SURFACE RUST IN THE CYLINDERS
THE PLOT THICKENS

bob lico · Post by **bob lico** » Jul 29th, '20, 10:42

considerable differance in numbers ,i run about 28 knots at 2400 rpm but my boat runs terrible in flat water which only occurs twice a season ,the boat drags so bad it feels like i am towing another boat behind me.boat will not run any faster than 13 knots plowing water like staying behind cresting waves coming in rough water inlet however the boat does not run between 13 and 21 knots it pops on plane and accelerates like a rocket. we get much better fuel economy than what you are reporting.

bob lico · Post by **bob lico** » Jul 29th, '20, 11:03

like i am trying to say they is good and bad with every advancement in technology . pretty bad when you travel with four or five other boats that cannot exceed 21 knots and you have to go a few miles up ahead than stop and make coffee and wait for them and you cannot ever follow a group of boats on a trip to montauk.we run 24-25 in 3 to five foot waves but boat slams in the cabin about even with head as boat hits crest of each wave .

Rawleigh · Post by **Rawleigh** » Jul 29th, '20, 12:36

Bob: I cannot even imagine what you are going through my friend! My thoughts and prayers are with you both!

bob lico · Post by **bob lico** » Jul 29th, '20, 17:15

RAWLEIGH i spent 7 straight days kneeling out side her window trying to teach her how to take eye glasses off the table and put them on and she puts them on under her nose and i cry internally. just so frustrating. i can make a Bertram attain 90% prop. efficiency but cannot teach a brilliant women basic movement.

Tony Meola · Post by **Tony Meola** » Jul 29th, '20, 23:16

Bob

Hang in there. Progress can be slow especially in these time when you can not have face to face contact. Keep working with her progress will come in time.

PeterPalmieri · Post by **PeterPalmieri** » Jul 30th, '20, 07:16

1962 31 wrote:CPL2280
I JUST POPPED A HEAD OFF 1 OF THE MOTORS NOT EVEN SURFACE RUST IN THE CYLINDERS
THE PLOT THICKENS

Great

bob lico · Post by **bob lico** » Jul 30th, '20, 18:54

thank you for the encouragement tony

1962 31 · Post by **1962 31** » Jul 31st, '20, 09:12

SHORT LIST OF PARTS NEEDED
CAMS AND LIFTERS
CRANKS POLISHED OR CUT
BEARINGS
OIL PUMPS
AFTERCOOLER HOUSINGS
SO FAR SO GOOD

bob lico · Post by **bob lico** » Jul 31st, '20, 14:35

ok i will bite why would you ever need crankshaft cut on a engine that submerged in fresh water not running!!!!!!

1962 31 · Post by **1962 31** » Jul 31st, '20, 14:39

TURNS OUT IT WAS SALT WATER WILL MOST LIKELY POLISH OUT NO HARD PITS JUST SOME STAINING MACHINE SHOP WILL MAKE THAT DECISION

Geebert · Post by **Geebert** » Aug 10th, '20, 16:37

im curious why larger, slower turning wheels are preferred to load the engine properly instead of smaller faster wheels, through higher, (numerically lower) gears. If you cant load the engine because a bigger prop wont fit, wouldn't that mean you need taller (numerically lower) gears?
1) Higher gears would give the prop a wider rpm range,
2)the lower pitch would slow the idle speed,
3) the smaller diameter would enable a shallower shaft angle
4) overall draft would be less

It always seems like people are gearing down (numerically higher) and using bigger wheels . what am i missing??

Carl · Post by **Carl** » Aug 10th, '20, 17:32

Geebert wrote:im curious why larger, slower turning wheels are preferred to load the engine properly instead of smaller faster wheels, through higher, (numerically lower) gears. If you cant load the engine because a bigger prop wont fit, wouldn't that mean you need taller (numerically lower) gears?
1) Higher gears would give the prop a wider rpm range,
2)the lower pitch would slow the idle speed,
3) the smaller diameter would enable a shallower shaft angle
4) overall draft would be less

It always seems like people are gearing down (numerically higher) and using bigger wheels . what am i missing??

Slippage or efficiently is the reason. Small wheels slip...think swimming barefoot compared to with fins.

bob lico · Post by **bob lico** » Aug 12th, '20, 11:00

you are missing half the sentence on your analysis -----yes biggest wheel that can fit plus a 1" BUT just as important you need PURE non agitated water flowing to the props. that the key to 90% efficiency. that is done by perfect flowing water around a 6" pultrusion from hull by the kevlar shaft log that has been glassed into the hull AFTER changing shaft angle and aligned.the boat must ride on the strakes and nothing to defused water flow like exposed transducer or ridiculous scooped thru-hulls.torque powers the boat not HP so to make her fuel efficient-cup-cup-cup got it

Geebert · Post by **Geebert** » Aug 15th, '20, 17:04

I must still be missing something. If the large props are required to push the boat because small ones slip too much, how are the 31's with twin outboard repowers able to go 50+MPH with 16 inch diameter props? I don't know what their pitch is, so i cant calculate their slip, but I've seen one boat with 300 Evinrudes
and one with 350 Yamahas. Both claiming 50 MPH, and both of those motors take a 16.5" max diameter if I'm not mistaken.

The Evinrude has a gear ratio of 1.85 with a max rpm of 6000 which means the most the prop spins is 3243 RPM. At 50 MPH with a theoretical 100% efficiency prop, would be 16.28 pitch
The Yamaha has a gear ratio of 1.73 with a max rpm of 6000 which means the most the prop spins is 3468 RPM. AT 50 MPH with a theoretical 100% efficiency prop, would be 15.22 pitch

With a 1:1 trans, there are a few diesels capable of that same shaft speed, HO Cummins, Yanmar for example. The Mercury TDI 370 can turn 4200 RPM.
The torque output of the diesels negates the need for stepping down the gears like the gas engines, as long as the torque on the shaft is sufficient to turn the prop at that speed.
So even if they were 24" pitch and slipping 30%, how would it benefit you to get 90% efficiency from the prop, while lowering your overall efficiency with a big prop.

Im not trying to argue against anyone, just trying to explain my perspective and learn what I'm missing if that's the case.
thanks for every ones input. i hope this isn't hijacking the op's thread

1962 31 · Post by **1962 31** » Aug 15th, '20, 19:22

No prob with hijacking bud
It's all learning and information

Tony Meola · Post by **Tony Meola** » Aug 15th, '20, 22:44

There are other factors that come into play, the biggest is shaft angle.

First let's take shaft angle. Depending on the year of the 31 the shaft angle if i remember correctly would be either 11 or 15 degrees.

The shaft angle on an out board and IO's is basically 0. Flat, making it more efficient at pushing the boat through the water. That makes the prop much more efficient.

If balanced properly the boat also runs flatter in the water changing the dynamics of the hull.

Then you have prop material, bronze vs nibral, vs aluminum vs stainless steel. Nibral has less flex than bronze, making it more efficient. Same for stainless over aluminum.

But all and all shaft angle is the biggest factor.

Carl · Post by **Carl** » Aug 16th, '20, 12:24

Geebert-

When a prop starts spinning faster another factor comes into play, friction and or drag. Big props and extra blades have lots of surface area that needs to be pushing through the water. So at a point spinning a big prop faster starts to work against you. Also faster boats will have less blades...a 3 blade is more efficient then a 4 blade and a 2 blade is more efficient then a 3. BUT then comes add more power and a 2 blade cannot handle having 1 of the 2 blades deal with 1/2 the motors power and blades start flexing and breaking so it's back to 3, 4 and 5 blade wheels.

Another factor...as boats go faster they rise up on plane and many continue to rise higher as speeds increase. Less boat in the water is less water to push out of the way, less drag so that small prop that was slipping a lot at slower speeds is not slipping as much.

I used the bigger prop is like wearing fins in the water...

Now I am going to ask you to think about making the best whirlpool you can in a 4' deep, round pool. best is described as the fastest water in the shortest amount of time.

Your given 2 Big Sumo wrestlers and 2 track runners.

Does everyone jump in and start going around?

Do you put the track guys in first running around fast as they can to get the water to start moving, wearing themselves out followed by the wrestles who don't move so fast....

Or do you have the Sumo wrestlers go in and slowly push through the water using their huge size and power to push lots of water and get things going. A couple times around these big guys are beat and can't go any faster, so they get out and the track guys jump in and start running around the pool pushing the flowing water faster and faster.

Geebert · Post by **Geebert** » Aug 16th, '20, 13:34

All points understood. Thanks for the responses. But let me take another swing and we'll leave egg beaters out of the discussion for the time being because we cant duplicate that shaft angle.
I think one thing at the heart of the discussion is how critical is shaft angle vs prop diameter. Increasing the diameter, to gain back your efficiency loss due to your high shaft angle vs decreasing diameter to decrease angle to gain back efficiency. If high shaft angles are to be avoided, than shouldn't large props also be avoided by using smaller faster wheels, so that you can decrease your shaft angle?

Gas boats are typically faster than diesels, and do it with smaller props. The diesels available now can do things the old ones couldn't, like high RPM, light weight, and fit in the same space.
I'll give you a theoretical combo based on one of the members of this board to illustrate my point.

Pete Fallon repowered his 31 express with 310 horse mercury 454 throttle body gas engines with 1.5:1 trannys, 17X19 3blade props and his top speed is 41.8 and cruise is 30MPH @ 3000RPM
The max rated RPM of those big blocks is 4600 RPM. 310 horse @ 4600 RPM is 354 LB-FT torque. Shaft speed at 4600 rpm with 1.5 trans is 3066rpm. 354 torque through 1.5 gear reduction is
531LB-FT of torque to the prop.
shaft speed = 3066 rpm
shaft torque = 531 LB-FT

for the theoretical repower lets use a Yanmar 6lpa 315 @3800 rpm
to make the yanmar match the shaft speed of Petes express we need to gear down to 1.24:1 trans, that gives us 3065 rpm shaft speed at max rpm.
315 horse @ 3800 rpm is 435 LB-FT. That torque through our 1.24 trans is 539 LB-FT to the shaft.
shaft speed = 3065
shaft torque = 539

Pete's cruise is 30mph @ 3000 rpm. With this Yanmar and trans, that rpm would be 2480 rpm @ the same speed, 30mph.
A yanmar turning 2480 rpm and moving 30 mph i think would get phenomenal fuel economy, which is the real goal here, not top speed. Top speed is just the indicator of hull efficiency. If you can go faster with the same or less power, your efficiency has improved.

The engines are similar in weight so our overall power to weight ratio is nearly unchanged, the shafting can remain the same because its "seeing" the same torque, the prop can remain the same because we have the same shaft power and speed.
This should give you a diesel that can keep up with a gas while burning less fuel, run cheaper props and shafts, none of the idle speed issues you get with big wheels, with cheaper engines than the 370s and up that some have, and they don't have the same top speed or cruise speed with their extra power

I think the advantage in this example is the low shaft angle made possible by the small props. This is why im confused about the large wheels just because its a diesel. shaft speed is shaft speed, applied torque is applied torque, gas or diesel doesn't change what the prop does.
I guess I'm still missing something.