Bob Lico & Others / Prop Help

[GerardA]

Hi Bob, et al;
This question came up on the B33 Site & I thought you as well as some of the other members here might offer some insight.
I have copied the thread below.
Thanks in advance.

Posted - 04/04/2016
Hi I'm new to the forum
Have had my '88 33SF for 2 years and are replacing the original 454 (340HP) with the 420 HP 6.2L Injected V8 (Gas). Torque is rated at 4600RPM and HP is rated at 5600RPM. Any suggestions for WOT target RPM for propping. Currently have 23 x 25 and 23 x 26 props available.
Al
WetProcess
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Posted - 04/04/2016
Al
WELCOME

I can't answer your ? but am incredibly curious as to how these small blocks handle the weight of our boats. Especially how they handle climbing the back of a wave.
Al

1978 33 FBC
NITES OFF
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Posted - 04/04/2016
Welcome aboard Al. You're definitely blazing a new trail with these engines. The manufacturer's specs should tell you a min and max range for WOT. I'd try and hit the high end of whatever that number is for longevity.

Regards,
Doug L.

1986 33 Bertram FBC
Cummins 6BTA's
Queen Elizabeth
Marblehead, MA
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Posted - 04/22/2016
The mfg specs for WOT (max) are 5600 rpm, but that is derived from the GM specs (which is max rpm of 6600!) for the LS3. Since they are not avail in reverse rotation, we needed to change from Velvet Drive to ZF trannys, which will run one fwd and one rev. I think 5600 is too high. Based on additional discussions with MarinePower we are going to target 5200 at WOT. Thankfully, there is enough space to swing big wheels, which are currently 23"dia. Will start with 25" or 26" pitch and see how it goes.

Re handling the weight:
The HP is rated at 425-430 and the torque is pretty flat from 3200 on at about ~400 lb-ft (peak at 4600 @ 435 lb-ft). Bear in mind the the old MIE 340HP's are 85 HP less, don't have orig torque specs handy and they are 200 lbs heavier (each!).

Will keep all posted
Al

WetProcess
Gulfport, FL
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Posted - 08/29/2016
FINALLY!!!! After 7 months and ~75K it's back in the water. Propping has been brutal(ly expensive). Been thru 3 sets so far and even Mich Wheel's recommendation (20 x 20 Nibral) was way off. The results are as follows"
Fully loaded (23,600#)
23 x 25p Bronze 4500 rpm/33 mph
20 x 20 Bronze 5400 rpm/27 mph!!!!
21 x 23p Bronze 4650 rpm/37 mph
20 x 25p Bronze 4750 rpm/38 mph
21 x 23 Nibral 4850 rpm/39 mph
Note idle speed 700 rpm/5.8 mph!!!(makes docking a lot more challenging)

Not 100% sure on rpm as these original tachs are not matching and at least one is off by >150 rpm. Having the J1939 NEMA 2000's to my Garmin display and will have a better feel. Trying to get the fully loaded RPM 5100 or above, so if I can verify the last round I'll try taking an inch of the Nibral props.

Cruising at 30 mph ~3600 seems effortless in a 2-3ft chop and the hole shot is UNBELIEVABLE. Pulling back necessary before I can even react!

I believe that part of the prop issue is related to the shaft speed. Since these engines are not available in counter rotation we had to go with ZF trannies. To get them in time (if I only knew the yard was going to take that long) we had to get 2.31:1 rations which means that the props are spinning at almost 2300 rpm at WOT. That makes the 70% radius speed >90 kts and the recommendation is not more than 60 kts. There is also a relationship here with boat speed, and many of the prop programs don't compute when a 40 mph top speed is entered into the equation.

I'd be really interested if anyone with solid prop knowledge has any ideas before I invest in another set of props or prop rework.




WetProcess
Gulfport, FL
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Posted - 08/29/2016

There's a fellow on the bertram31.com forum who is extremely knowledgeable in this area.
His name is Bob Lico.
There are lots of other members with experience as well.
If you post a thread over there you will get some recommendations.

Gerard
FREEDOM
86 SF 454 Merc
Green Pond, Falmouth MA
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Posted - 08/30/2016
Thanks for the suggestion. I do need however to correct a typo...the current prop is the Nibral but it is a 21 x 25p speed and RPM are correct. Not sure how to move the post over so I will try contacting by email if possible.

WetProcess
Gulfport, FL

[Tony Meola]

Bob is the best to answer, but they need to add cup, not pitch.

I would have stuck with the 23 inch prop if there is room, reduced pitch to get the RPM's up as much as possible, may need to over rev then added cup to offset the reduced pitch and would have reduced RPM's to the RPM's you need to have them running at but picked up speed. A good prop shop should have been able to help with this.


This one is blazing new territory. I think the engines will work too hard pushing that boat, but Bruce or Bob can answer that one since they have the most knowledge in this area.

[Carl]

The gentleman is all over the map.

First thing I'd do is get working tachs.

Then I'd need to know a firm WOT...
I believe we have GM@ 6600, mfg@ 5600.
Marine Power came in at 5200rpm, "after discussions", what does that even mean?
Even with that owner is striving for 5100....??


My experience...owner is hearing what he wants to hear, wants fast over longevity...till motor dies.
I have found Talks tend to go like this...

Marine Power(MP)- "yes you need to hit 5600rpm at WOT".

Owner(O)- "Does it have to be exactly 5600 or is there some wiggly room."

MP- "If your 100-150 below, you should be okay"

O- "So 5450 is OK?"

MP- "Yes, it should be okay."

O- "What if really loaded and can only achieve 5300?"

MP- "Ummm...guess you'd be okay for a bit till you burnt some fuel, but really 5600."

Owner takes away -- Okay 5300 it is....and if I'm 150-200 below I'll be fine, yup they said 5100 is good.

I could be 100% off base here...but in his words 5200 WOT from marine power and he's striving for 5100...and tachs are out.
Concern "seems" to be over speed.


For me

What I want to know is "IF" the engine blows...who stands behind their WOT number.
Stand behind as in will replace blown engine and not say, motor was overloaded, over propped not covered.
I then use those WOT numbers.

Without working tachs and a definite WOT its a crap shoot.



Next...
20 x 20 is way off?
Maybe I am wrong...but that is the only set I see as being correct...yes speed is down, but 5400rpm.
Which according to owner with tach 150rpm off could be as high as 5550 or low as 5250.

If I was at this point...20x20 @ 5400...I'd stop and get tachs calibrated...change for new...verify the WOT.
Anything else is just guessing and hoping.


Worth saying again:
Without working tachs and a definite WOT its a crap shoot.


Then check numbers again. If in WOT ballpark, its time to start tweaking prop diameter, style, blades, material, cup, rake to achieve WOT and bring that speed up...if possible.
In my book the WOT takes precedence then we turn to performance.


I stopped playing with customers props for just this reason.

[bob lico]

step one Calm down! step two believe none of what you hear and half of what you read on prop wanna beee. ok lets get a positive starting mark by simple timing light on engines (with vacuum disconnected and pluged) to verify BOTH tachs. prop tech is very expensive if your buying props to experiment.i had a couple hundred at my disposal and two fork lifts capable of lifting a 38' boat out of water on concrete pad and change props in 10 minutes and drop back in.i am retired and will try to point you in the right direction. the ultimate answer is a two speed ZF transmission to lower idle speed with high speed cruise ,trolling valves are out of the question they are not made to dock a boat (repeaded forward,reverse) so lets get to propping a LS small block.to get to proper rpm to load we do not just up and up pitch------wrong 25/26" pitch is way out of line! off course you have 6mph idle speed.the answer is cup, cup and more cup, better yet a varable pitch and cupped.loaded SHOULD be 5700 loaded not 1 rpm less.just for test afterward don`t exceed 4000 rpm. 21" to 23" varable pitch with full cup i would tell you to rake 4 degree but prop shop will not listen or will not comprehend for inboard use.i am not in favor of LS small blocks in a 33' boat this is diesel only. torque not horsepower is the key to a boat of that weight.BTW. is this a 6.0 or 6.2 LS motor?

[GerardA]

You guys are awesome!
Thanks for the fast response!

[Carl]

Bob--

Agree with getting tachs right on.
Agree with achieving 5700 WOT.

Assuming if starting to complain about wheel cost a two speed tranny is out of the question.


Confused past that point...making assumption the tach is right for now.

Square 20's are only attaining 5400rpm

Increase to Variable pitch 21-23", add cup, add rake...they all eat power and he is already 300rpm under WOT.

Where does he get the additional rpm to offset those modifications?

If 4 blade, go 3?
Reduce diameter?
Reduce pitch?
or Go Nibral?


Reduce pitch and add cup would be my starting point.
But all guessing till tachs are right.

Not arguing...just trying to understand and learn your thought process.
Mine has been to keep simple and safe over chasing customers dreams of achieving huge improvements.

[bob lico]

carl-----------yes,yes,yes,and yes and yes bottom end torque sucks compare to cummins QSB-420hp diesels. and yes huge trim tabs to get that baby on plane loaded. yes i would play safe at 20".

[Carl]

bottom end torque sucks compare to cummins QSB-420hp diesels.

While true...no diesels in the picture, 6BT's even a nice choice, or 6BTA's. However, it looks like he pulled Big block 454's out for the small blocks...he's up 85hp but loses 85lbs of torque, even more if using his numbers.

Big tabs to get over the hump, yes...but that's not gonna help climbing up the back of a wave, needs to be able to spin them props uphill first...torque. Smaller wheel or more gear reduction.
Like to hear how it plays out.

2 Speed...nice idea...get over the hump, shift and go.

[bob lico]

carl in my old age i become relundant to judge to quickly. some years back this guy came into marina and ask my prop advise;" i have the fastest fishing boat and will use it to go to hudson canyon (72 miles out of fire island inlet) ok lets sea the boat before giving my opinion .low and behold a beautiful 32' catermarian built near bruce`s shop in FL. looks identical to Skater Cat. for power two 500 hp yammar diesels , as we went down river i look down at levers for gear shift between the front seats -----huh!!! three speed gears . he took it up to twenty with black smoke pouring out the transom shifted into second and the boat went up to 92 or 93 mph and settle back down to 68 mph cruise. yes quite fast for a fishing boat .built a set of props to break 100 and cruise at 72mph. so i am a believer on two speed ZF for fishing boat and thats exactly what Cabo did with 350hp cats in there 30footer. the main benefit was a 4 mile a hour idle speed and jump on plane.carl never say never but in this case and don`t be led astray i fully aware of the twin turbo 1500 hp 6.2 LS motors but thats pushing a 3000 lbs car not a 20,000 lbs boat lets put a ZO-6 corvette 650 hp in a 18 wheel tractor trailor going up hill and see what happens.i can only see running the balls out of those engines with high tuned 3 blade Ron Ellis props. but the engines will not last!

[Tony Meola]

Bob

I agree, I don't see these engines lasting very long. Not set up right for that size boat.

[Navatech]

If I've said it once I've said it a hundred times... The more HP you squeeze out of the same physical size engine (let alone a smaller one) the less longevity you'll get out of it...

There's a reason a 1,000 HP marine engine is more like triple if not quadruple the size of two 5 liter something GM LS (small block) engines pumping out 500 HP each!... And the reason isn't only the fact that Diesel engines are built heavier...

The US Army wanted more HP for the Abrahams then was possible at the time with Diesel technology... They also wanted to shed some of the weight... So they went for gas turbine (essentially a jet engine) technology... An added advantage is that the gas turbine is a lot more flexible in terms of the fuel requirements...

[Carl]

To play devils advocate...

I think the engines could last in a 33. But it would be a choice of running conservatively, meaning gear the thing down and not try to make it into a speed demon so you have the low end torque to get over the hump, climb waves with a bit of reserve. Yes, the drawback a slower cruise, slower top end...but the trade off is some longevity.

It's been done for years...boats up to 40' with gas big blocks...they were not high hp, but had the torque. But that was also when boat owners cruised happily at 16-18knts. Now we have lighter high hp motors with less torque...spin em faster with more reduction gains the torque back...but speed is the killer...today everyone wants fast.



Look at our 31's...they originally came with diesel options of GM 140hp and the big hp diesel was the 170hp Cummings or gas started with only 225hp motors and for the speed demons went up to 325hp

Today, how many guys even consider the Cummings 210hp motors...discussion is between the 270's or 315's. Yanmar 210's great motors for the 31...but considered a slower cruise boat.

[Tony Meola]

Carl

My 75 came through with 454 350HP blocks. Cruise was around 19 knots at 3000RPM's. In 1975 there was very little around that could run with us. Outboards were topping out at 100HP and there were not many twin outboards around.

If we fished a tournament we could go father in less time than most others but today, that 19 knots is slow. Personally I think the 31 hits her sweet spot at around 25 knots. Hence the choice to boost HP a little.

Today, unless you do what Bob did, they are not going to be speed demons but will run with the best of them.

Big Block gas engines in anything stretching over 30 feet was always questionable due to the added weight. Burns more fuel and doesn't come out of the hole well.

I don't think this one will ever really prop right to get the owner what he wants out of her.

[Carl]

Tony- I was pulling info from a 60's brochure. Your right as years went by they added higher power options. We were brought in to do the running gear on an early 3208T conversion...one of the first 31 canyon runners around that we know of. Boat was considered super quick at the time with a 25knt cruise.

Carl

Big Block gas engines in anything stretching over 30 feet was always questionable due to the added weight. Burns more fuel and doesn't come out of the hole well.

True, gas in big cruises is questionable in my mind as well...but they put them in and many boats still have them...some have stood the test of time. Case and point, friend still has his Chris Craft 42' Sport Cruiser from 69-70 with original gas 502 interceptors, heavy boat. He used to run yearly to Martha s Vineyard, Block Island, Montauk and fished Mud hole regularly from Staten Island...so those motor saw a good amount of running for years. They still run pretty well...sort of. Hard to tell as the last years boat went in water, it went from the well to the slip and back at the end of the year. He was never quick, but the boat moved and yes it burnt fuel...but fuel was still cheap [/quote]

I don't think this one will ever really prop right to get the owner what he wants out of her.

I'd agree owner will have a hard time propping.

I'll disagree also...
I know the boat can be propped correctly, he's already in the ballpark with the 20 x20's. I'd start dialing in around those wheels.


The reason "owner" will have a hard time propping, I think he has a different cruising and top speed numbers in his head because motors weigh less and have more hp, while disregarding the lost torque.
The other problem...to dial in props you need the true recommended WOT spec and accurate tachometers. Owner has been at this for a good long while and still has neither.


One of my favorite customers had a saying that has always held true..."Speed Costs"

[bob lico]

carl my advise on 21" to "23" varible pitch is a three blade with a uncommon ear shape instead of round they are more pointed like cleaver props of mercruiser fame they are orientated to gas power and take less torque to drive.for comparison look at yesteryear high performance outdrive props on 454" gas powered 32'' boats with dual mercruiser out drives.thats the trick to let him get his required 5600 rpm yet get that beast over the hump with gas motors and 3' wide tabs. i hate trying to fix a screw up rather then plan ahead!.

[Tony Meola]

Carl

At one point the ,3208's were an option. Fred Haas from tackle direct has one. A great ridding 31. She sits much lower in the water do to the weight of the engines. She does not ride over the waves, she plows through them.

[bob lico]

tony i have partnership in 3208`s at 435 hp each in a 38' bertram .fitted her with 3 blade because already has massive torque.purchase for repower but nothing wrong with engines install in the 1995 and use as gambpling boat tie to dock for 10 years.

[Tony Meola]

tony i have partnership in 3208`s at 435 hp each in a 38' bertram .fitted her with 3 blade because already has massive torque.purchase for repower but nothing wrong with engines install in the 1995 and use as gambpling boat tie to dock for 10 years.

Those 3208's are bullet proof. How fast is that 38?

[Carl]

carl my advise on 21" to "23" varible pitch is a three blade with a uncommon ear shape instead of round they are more pointed like cleaver props of mercruiser fame they are orientated to gas power and take less torque to drive.for comparison look at yesteryear high performance outdrive props on 454" gas powered 32'' boats with dual mercruiser out drives.thats the trick to let him get his required 5600 rpm yet get that beast over the hump with gas motors and 3' wide tabs. i hate trying to fix a screw up rather then plan ahead!.

Right you mentioned Ellis wheels, long overlap blades. Have a pair from dads boat, great wheels but cavitation creamed them around hub on his. Mine with same power I could not even get on plane. He's a 28' Hatteras, heavy but flat bottom...

[Carl]

Those 3208's are bullet proof. How fast is that 38?

I'd argue bulletproof at 435 hp

[Carl]

Carl

At one point the ,3208's were an option. Fred Haas from tackle direct has one. A great ridding 31. She sits much lower in the water do to the weight of the engines. She does not ride over the waves, she plows through them.

Yup, Bertram option later on...


Definitely heavy

[bob lico]

the 38' Bertram is very sentimental to me because the Capt. built the bridge. flawless F/G wrap around bridge with his pod with single lever controls.has nice walk thru on starboard side to a four place seat in front of bridge.excellent design.he also design and built fish prep area along main bulkhead in cockpit.i wanted to upgrade to 550 hp QSC cummins with fancy props. so we ran the hell out of those 435 cats with ZF gears from maryland to just shy of statan island ny.cats ran well so rather senseless to put out.she runs 26 knots with 4" of crap on bottom. i realize some people call this hyjacking but i could care less it honors a genius that was the most talented F/G craftmen i have ever witnessed.

[Carl]

. i realize some people call this hyjacking but i could care less it honors a genius that was the most talented F/G craftmen i have ever witnessed.

Bob-pictures please.

What's to highjack? Question was answered in 1sr couple posts. No feedback from OP and thread morphs as they almost always do in any conversation.

[bob lico]

carl--------cavitation dril 3/16" hole on each blade about 1/2" from hub. you and i share when someone says prop has 23" pitch another has 22" pitch therefore the former will drive the boat faster. NOT TRUE first what shape are the blades people just can`t make this blunt statement .you can work with the shape of the prop for to take advantage of big torque diesel however gas motors have to rely on a higher rpm to take avantage of whatever torque it has. my words are strickly inboards, outdrives are totally different especially with todays 4 blade clevers. LS 6.2 might even consider 19" dia with 4 blade cupped to the max as a uncoventional approach. hard to advise when the guy purchasing the props.and in and out charge from boat yard

[GerardA]

Tony, Carl, Bob & Nav,

Thank you for your responses.
Like Carl I'm disappointed we haven't seen any response from Al yet.
I'm still hopeful.
I posted this here on behalf of AL as I find your prop discussions very interesting & educational.
The give & take is one of the things that makes this board special.
Keep up the good work.
Thanks

Gerard

What are your thoughts regarding this approach to gas re-powering?
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Hi Gerard. Your buddies have some pretty good ideas and seem to have a handle on props, torque & HP. My solution to the 2 speed gearbox is cam timing. I think I've gone over this a few times before you joined us. I took a pair of new 8.1's and tore them down & rebuilt using a few racing techniques to get more HP and advanced the cam timing about 1.5 degrees. This makes the same engine that used to have it's maximum torque at 5400 now produce the same amount of torque at 4000. This enables you to climb out of the hole like there's no tomorrow and although I'm not attaining the top end speed that Al is, (He's also talking MPH & not Knots), I can reach about 33 knots at 4000 and cruise comfortably at 25 at around 3200 (fully loaded water, fuel & people) & I'll guarantee you that I'm burning 1/2 the fuel that Al is.
I think I can also safely say that I believe my engines will last longer at 3200. The engines dyno'd at 400HP when they left the shop and I'm turning 21 X 21, 4 blade Nibral's.

Joe

[Carl]

Auomotive or marine racing technics?
Might be worth mentioning, some cams cause motors to suck up water thru exhaust when shut down. If already addressed, no harm, if not something to be mindful of.

What is reccomended WOT, are you attaining at least that RPM loaded?
Cruise speed, mpg, mph, knots, hole shot means little.

Tachs correct?

[bob lico]

do you really think advanceing the cam will make that 6.2 a marine engine? ok then i will build another 408" 525 hp chevy small block and use the pair in my 31 Bertram seriously i have a 4 degree advance on the Lunati roller cam in this build and it made little change then straight up installation.made very little difference on dyno . my corvette has 10.86 ration in first gear (3.06 in trans and 3.55 read differentials ) you would feel quite a bit more acceleration changes then your 2.53 ratio in boat. cam timing is not the answer.

[GerardA]

Bob,
I was not intending this to improve Al's 6.2 engines.
My question was your opinion of doing this to an 8.1 for a B33 SportFisherman.
Thanks
Gerard

[bob lico]

yes it will lower the peak HP. as well as torque RPM. 4 degrees advance will lower the torque curve peak about 300 rpm assuming you are using cam spec. close to those of 5.3 LS roller cam motor. like i indicated with a 10,000 lbs planning hull we can make it work but 20,000 lbs is real asking much more then this fabulous SBC was intended for. so many advantages over big block with cross bolt mains and cylinder head design, injection,one piece seals but not for this application.

[Wet Process]

Gentllemen (I think that still applies to boaters)
Thanks for all the input. Just to clear things up I wanted to repeat the post that I put on the Bertramm 33 forum:
Gentlemen,
Thanks for all the info. As far as definitive info--MarinePower (MP) in writing advised me to prop out the engines at 5200+/- 100 RPM. MP's spec for the engine (GM's spec doesn't count as it is fully marinized using MP's MEFI 6B program for the ECM). They warranty the engine for 5 years with the submission of the warranty sheet with performance #'s signed by the dealer (Elite Marine here in St Pete, FL). The initial speed estimate was from the installer (40 mph WOT) I will be happy with a 30 mph cruise at good fuel economy, which I am estimating at between 3500-4000 rpm.

The very first run with the original 23 x 26p props was infract 38 mph but 4500-4600 rpm (not full fuel). From that point we tested fully loaded as shown in the earlier post with all the prop sizes reported originating from reqorked 23 x 26p props (I had 4 of them). The 20 x 20p was a used set borrowed for testing. The props now on the boat are Nibral 21 x 25p and after 18 hrs of varied break in running are running 36-37 mph @ 4900-5000 RPM WOT. The bottom line is that MP doesn't think that we really need to get all the way to 5400.

The stbd tach is within 50-100 rpm and we are using both Fluke and ESI inductive pickup tachs for all testing. New tachs are on order.

The engines certainly do not feel overloaded and MP warrants them in this application for 5 years as I said, so I don't think this is to far out of line (small block/big boat). After ~18 hours of break in operation we seem to have picked up ~100-150 rpm at WOT to 4900-5000 but lost some speed (36 mph vs 38) but I have also put all the fishing gear, inboard trim panels, etc back on the boat. Based on all the discussions I am thinking the next step is to take 1" out of the pitch.

The two local prop shops won't go more than 2" off pitch (3 after fighting) or diameter (no wiggle room). Making to great an adjustment will also affect blade shape and efficiency they say (true). The 21p x 23d props used in the early testing started out at 23 x 26 so That's what prompted the 21 x 25's that became available. I'll work my way down and add cup as necessary. I am still curious as to why I cant go with the larger diameter and work pitch and cup or if it would be benefical.

Having engine data NEMA 2000'd to Garmins in the next few weeks to have as accurate as possible data on rpm, fuel consumption, etc.

WetProcess
Gulfport, FL

[Carl]

Marine Power Stands behind 5200 +/-100 WOT and will warranty that. Good.

Tachs within 50-100... me, I'd like to see you hit 5300-5400 loaded.
If you know tachs are 100%, I'd be comfy with hitting 5300 loaded.


Slightly confused from here:

You are running Nibral 21 x 25 wheels and getting 4900-5000 WOT. You need 3-400rpm

That would mean Nibral 21 x 23 wheels would get you there everything else being equal. Here's the confusion...you said you ran the 21 x 23 wheels in both Bronze and Nibral, bronze at 4650 and Nibral at 4850 WOT???

Were the 21 x 23's checked to be what was stamped on them? Cause going down 2" in pitch in a similar wheel does not lower WOT.
Or did 21 x23's have cup, added rake, another blade...or maybe just out of adjustment.
Something is off...


My .02...you need to have a baseline of what works to achieve your WOT.
Then you tweak wheels for performance using those numbers.





Larger diameters are more efficient to a point...then friction and drag of larger wheels work against you. Same going 4 blade over 3...more blade drag. Gas motors have less torque so spinning wheels faster is a way to gear down and use available power.