Diesel engines in speed boat
10-10-2008, 04:44 PM
#301
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fact5,
What boat do you have?
The 38 was like that but the 46 had too much exhaust to put through 100%.
The 38 & 46 pleasure boats were like yours. It's a good set-up and works well but it's still to mask the fact that the engine has no Hp at low speeds.
Your just creating slip to allow the engine to accelerate to a point where the engine starts to make boost. Once the engine has some boost it can now overcome the drag/resistance the prop has on it from the increasing rpm's and the boat starts to move and once the wake leaves the transom the effect of the exhaust is now zero.
I'm going off on a tangent here but.............
It goes back to several statements I've made on here and what it takes to have a really successful performance diesel business. That is "Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance." This came from Craig Barrie talking to a VP of Cummins and myself back in the 80's and it is as true today as it was then.
Until you can do all those things diesels will just be a novelty for those who like the fact they have diesels.
Joe Gere
What boat do you have?
The 38 was like that but the 46 had too much exhaust to put through 100%.
The 38 & 46 pleasure boats were like yours. It's a good set-up and works well but it's still to mask the fact that the engine has no Hp at low speeds.
Your just creating slip to allow the engine to accelerate to a point where the engine starts to make boost. Once the engine has some boost it can now overcome the drag/resistance the prop has on it from the increasing rpm's and the boat starts to move and once the wake leaves the transom the effect of the exhaust is now zero.
I'm going off on a tangent here but.............
It goes back to several statements I've made on here and what it takes to have a really successful performance diesel business. That is "Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance." This came from Craig Barrie talking to a VP of Cummins and myself back in the 80's and it is as true today as it was then.
Until you can do all those things diesels will just be a novelty for those who like the fact they have diesels.
Joe Gere
10-10-2008, 08:40 PM
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10-10-2008, 08:51 PM
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When we built the 46 Cougar "Spirit of America" with the triple Cat 3176's (then converted to 3196's) & ASD-10's (1.6:1 overdrive) back in the mid/late '90's, we had the same problem with the propeller curve absorbing more horsepower at pre-boost RPM than the electronic engines could produce and therefore not get into boost and over the hump. We went back to the old technology of a vent tube to aerate each prop to allow them to "slip" and get the engines into boost. We tested with different diameter vent tubes to get to a happy median between the slipping propeller and "hole-shot".
One thing we learned during testing was if we put a large enough vent tube to allow the engines to spool up and then mechanically shut-off the air supply to the vent tube with a device (flapper valve) that could withstand the suction of the propeller during the transition the boat hooked up immediately and the hole -shot was incredible.
Two things to keep in mind is that the flapper valve only needs to resist the forces of the suction from the wheel until the boat gets on plane and then both ends of the tube are ventilated and there is no force on the valve and the driveline/drive system needs to be capable of resisting the shock (especially from an electronic engine with an aggresive torque/HP curve) of the peak torque at the instant the air is shut off from the prop.
The only reason I throw this out there is that in our situation it turned out to be a more economical solution to maximizing hole-shot without further complicating a highly engineered induction system.
10-10-2008, 10:42 PM
#305
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rush,
Agreed that is easier but doesn't solve the real problem.
Do you have pics of that Cougar? I don't remember that boat, how did it run?
But, I'll refer back to my earlier statement:
"Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance."
You can't vent a Bravo style drive, then again the smaller dia props may slip enough to get the engine off idle and building boost?
You know that's why gas engines work great with those little props, they can start to get into their power band before the prop becomes efficent.
Let me make a little money here if the market doesn't take it all and I build something to play with and we'll do real testing again!!!
Joe Gere
Agreed that is easier but doesn't solve the real problem.
Do you have pics of that Cougar? I don't remember that boat, how did it run?
But, I'll refer back to my earlier statement:
"Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance."
You can't vent a Bravo style drive, then again the smaller dia props may slip enough to get the engine off idle and building boost?
You know that's why gas engines work great with those little props, they can start to get into their power band before the prop becomes efficent.
Let me make a little money here if the market doesn't take it all and I build something to play with and we'll do real testing again!!!
Joe Gere
10-11-2008, 04:04 PM
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rush,
Agreed that is easier but doesn't solve the real problem.
Do you have pics of that Cougar? I don't remember that boat, how did it run?
But, I'll refer back to my earlier statement:
"Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance."
You can't vent a Bravo style drive, then again the smaller dia props may slip enough to get the engine off idle and building boost?
You know that's why gas engines work great with those little props, they can start to get into their power band before the prop becomes efficent.
Let me make a little money here if the market doesn't take it all and I build something to play with and we'll do real testing again!!!
Joe Gere
Agreed that is easier but doesn't solve the real problem.
Do you have pics of that Cougar? I don't remember that boat, how did it run?
But, I'll refer back to my earlier statement:
"Surface Drives are great but to be successful with diesels you have to be able to replace the existing gas engine without modifying the boat's structure, hook-up to the existing Merc drives and give similar performance."
You can't vent a Bravo style drive, then again the smaller dia props may slip enough to get the engine off idle and building boost?
You know that's why gas engines work great with those little props, they can start to get into their power band before the prop becomes efficent.
Let me make a little money here if the market doesn't take it all and I build something to play with and we'll do real testing again!!!
Joe Gere
You threw the "Bravo" word out there again. We know the Merc poster child for a high performance diesel is the Cummins QSB. But as we all know the QSB has enough torque to tear a Bravo to bits with ease. The NXT isn't even rated high enough to handle the input torque of a QSB 480. Good ole big dog #6 drives are the only thing off the shelf to handle that much torque. Uncle Sam had a good go around with Cummins 6BT engines mated up to Konrad drives and that kinda quietly withered away. What we need is a Bravo "D" model. Take the Bravo 1 case and fill it up with some beefier parts and maybe we would be able to have that marketable package. Or mabe Merc could just start building TRS drives again.
10-11-2008, 06:48 PM
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The original 3196's where set at 800 HP and the last set at 900 HP. The boat ran strong mid 80's full fuel or empty didn't matter.
On another note:
I am close to moving ahead with updating my 5.9TA 300's in the 40SH with QSB425's (420 BHP @ 3000 RPM). I have looked at the capacity of the original 5061's (1.15:1) and ASD-8's that you guys originally built the boat with and they have plenty of capacity. I still need to review the driveline sizing but an upgrade here will not be a deal breaker.
At 12,000 lbs (half fuel) and a current 52.4 MPH top speed do you guys have any guestimates on performance with the new configuration? I have done a few calcs and am just curious where my formulas fall compared to all yours.
I would also be curious if Rik would like to chime in with a ballpark prop suggestion. I am currently spinning 17 x 28.5 Rolla 4-Blades.
Rich
10-11-2008, 07:30 PM
#309
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Rush,
RIK is much better at real world estimates with today's technology, reach out to him he's helpful.
Firefox,
I say this with all respect, your wrong!!! Look what I always write and we did it 20 years ago, yes with TRS's but Bravo's would have worked just fine -
"I want to build a diesel race boat again, I'd love to build a Buzzi bullet type boat. Single engine, 30 Phantom or similar (Maybe a Bat Boat?) with an outdrive and use a Lenco step-up box again inside."
When you use a step-up or overdrive box you reduce the torque and increase the drive input shaft speed - the little black drives work!!!
I have two projects in the works now that, well the economic downturn have slowed down drastically but if I can get them going - I'll get the boat, put in a box w/bravo drive and document it on here as well as race it.
I can be bold about this because we did already and I don't understand why people have abandoned it again?
Joe Gere
RIK is much better at real world estimates with today's technology, reach out to him he's helpful.
Firefox,
I say this with all respect, your wrong!!! Look what I always write and we did it 20 years ago, yes with TRS's but Bravo's would have worked just fine -
"I want to build a diesel race boat again, I'd love to build a Buzzi bullet type boat. Single engine, 30 Phantom or similar (Maybe a Bat Boat?) with an outdrive and use a Lenco step-up box again inside."
When you use a step-up or overdrive box you reduce the torque and increase the drive input shaft speed - the little black drives work!!!
I have two projects in the works now that, well the economic downturn have slowed down drastically but if I can get them going - I'll get the boat, put in a box w/bravo drive and document it on here as well as race it.
I can be bold about this because we did already and I don't understand why people have abandoned it again?
Joe Gere
10-11-2008, 08:05 PM
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Rush,
RIK is much better at real world estimates with today's technology, reach out to him he's helpful.
Firefox,
I say this with all respect, your wrong!!! Look what I always write and we did it 20 years ago, yes with TRS's but Bravo's would have worked just fine -
"I want to build a diesel race boat again, I'd love to build a Buzzi bullet type boat. Single engine, 30 Phantom or similar (Maybe a Bat Boat?) with an outdrive and use a Lenco step-up box again inside."
When you use a step-up or overdrive box you reduce the torque and increase the drive input shaft speed - the little black drives work!!!
I have two projects in the works now that, well the economic downturn have slowed down drastically but if I can get them going - I'll get the boat, put in a box w/bravo drive and document it on here as well as race it.
I can be bold about this because we did already and I don't understand why people have abandoned it again?
Joe Gere
RIK is much better at real world estimates with today's technology, reach out to him he's helpful.
Firefox,
I say this with all respect, your wrong!!! Look what I always write and we did it 20 years ago, yes with TRS's but Bravo's would have worked just fine -
"I want to build a diesel race boat again, I'd love to build a Buzzi bullet type boat. Single engine, 30 Phantom or similar (Maybe a Bat Boat?) with an outdrive and use a Lenco step-up box again inside."
When you use a step-up or overdrive box you reduce the torque and increase the drive input shaft speed - the little black drives work!!!
I have two projects in the works now that, well the economic downturn have slowed down drastically but if I can get them going - I'll get the boat, put in a box w/bravo drive and document it on here as well as race it.
I can be bold about this because we did already and I don't understand why people have abandoned it again?
Joe Gere
Ive seen TRS drives survive because they go through a gear box before the drive. So that makes sense of what you say. But then the question pops up if you have a gearbox why do you need a shiftable drive? Why not just build a Bravo with no cone clutch and let the gear box do everything else?
Last edited by 29Firefox; 10-11-2008 at 08:10 PM.
