Performance Boats Forum banner
1 - 17 of 17 Posts

·
Amatuer
Joined
·
241 Posts
Discussion Starter · #1 ·
I have searched here, old hb forums, and google and have not found what people generally consider the ideal setup for a v-drive for speed. Here is a crude picture.



We can assume a 20 foot boat for simplicity or just give measurements as percentage from transom. It seems like most people consider the less angle the better with 8 being the target lots want to hit, but the others?

angle = 8 degrees
cg = ?
v = ?
p = ?
r = ?

Just from eyeballing pictures it looks close to the following

angle = 8 degrees
cg = far back as possible?
v = 40%
p = 20%
r = 10%

Does that seem right or is there a website that explains all this?
 

Attachments

·
Hard Core Member
Joined
·
406 Posts
This can be discussed endlessly, but there is no set answer. If anything can be said, the shape of the bottom of the boat is more important than all of the above. A boat with a hook in the bottom won't go fast no matter what you do to it. A boat with a rocker shape will run nose high with minimum wetted surface but will be more sensitive to all of the variables. When everything is right, the force from thrust vs. the center of resistance is in balance and the boat will run without bouncing or nosing over.
DJ
 

·
Registered
Joined
·
1,640 Posts
This is going to sound more critical than I mean it to, but answering your question would be akin to stating what is the ideal setup for a rear drive car. You can imagine all the different applications.

If you narrow your query to a specific hull, desired performance level, and intended use, you can get some useful feedback. ;)
 

·
Amatuer
Joined
·
241 Posts
Discussion Starter · #5 · (Edited)
This is going to sound more critical than I mean it to, but answering your question would be akin to stating what is the ideal setup for a rear drive car. You can imagine all the different applications.

If you narrow your query to a specific hull, desired performance level, and intended use, you can get some useful feedback. ;)
My amatuer-ness is obvious.

This is the hull http://www.glen-l.com/designs/inboard/bandido.html , it's not completed(4 more years), but its at the stage where I have to decide on powering options.

Here is a rough sketch for how the plans recommend setting it up with a single engine v-drive option. The prop is a 16 inch prop.


I would like to be able to hit the mid 70's. I would think it would be doable since another guy has done 76 in that hull with twin 200hp outboards.
 

Attachments

·
Registered
Joined
·
1,640 Posts
Start thinking in the 600+ HP range. One option to keep static compression down, would be to go with a 8-71 supercharger, dual carbs, wet thru transom exhaust, and a fairly mild roller blower cam. You could go faster, but the idea behind my suggestion is a reliable high performance engine that could cruise in the 70+ range without wringing the engine out. In addition, you would have the "out of the hole" power that will serve you well with full loads of people and gear.

Another thing that will help with heavy loads is a 1/4" stroker crank, as in a 496 cubic inch. The longer stroke provides more leverage against the connecting rods. It does not cost any extra if you build it this way from the outset.
 

·
Amatuer
Joined
·
241 Posts
Discussion Starter · #7 · (Edited)
Start thinking in the 600+ HP range. One option to keep static compression down, would be to go with a 8-71 supercharger, dual carbs, wet thru transom exhaust, and a fairly mild roller blower cam. You could go faster, but the idea behind my suggestion is a reliable high performance engine that could cruise in the 70+ range without wringing the engine out. In addition, you would have the "out of the hole" power that will serve you well with full loads of people and gear.

Another thing that will help with heavy loads is a 1/4" stroker crank, as in a 496 cubic inch. The longer stroke provides more leverage against the connecting rods. It does not cost any extra if you build it this way from the outset.
That's sounds excellent. Thanks.


Not in anyway ungrateful, any opinions on departing from the plans and changing the strut angle from 12 to 8?
 

·
Registered
Joined
·
1,535 Posts
Amm, very interesting project you have going. Do you already have the hull. Got any pics? As for HP needed to push the boat into the 70's with the v drive conversion, I think you will need close to 700hp to get a 30 ft vdrive into the mid 70's. There are plenty of sterndrive boats in that range that take 600 or more to get there. Just curious, without the ability to trim the boat, how it will handle? I'm sure tabs can help, but they add drag.






Darrell.
 

·
Highaboosta
Joined
·
3,431 Posts
My inexperienced opinion.
Getting the bow up is going to be the biggest challenge with a hull that big.
The engine all the way back and the strut forward a good distance from the transom is probably what is going to be needed.

I feel the balance of my boat is real good but a significant v drive disadvantage is apparent.
Under hard accelleration the boat airs out great, probably better than most.
At a steady cruise speed the hull rides real flat and will want to porpoise a little until I give it a little down plate.
This is certainly because of not being able to trim the drive to keep the bow up at steady cruise speed.
I'm getting stern lift but not bow lift.

That big of a boat would probably be better off with an I/O.
 

·
Amatuer
Joined
·
241 Posts
Discussion Starter · #10 ·
Amm, very interesting project you have going. Do you already have the hull. Got any pics? As for HP needed to push the boat into the 70's with the v drive conversion, I think you will need close to 700hp to get a 30 ft vdrive into the mid 70's. There are plenty of sterndrive boats in that range that take 600 or more to get there. Just curious, without the ability to trim the boat, how it will handle? I'm sure tabs can help, but they add drag.

Darrell.
I still have a lot of work to do(4 more years I estimate), but here are a few pics...



The next step is to build the transom and the two foremost frames. I need to decide on a powering option before I move on. The stringer system is different between single and twin engine versions. The single engine v-drive option sounded good to me, but I have yet to even see a picture of a fast v-drive this long. Looks like I/O's and outboards dominate this class of boat.
 

·
Hard Core Member
Joined
·
406 Posts
I'm no expert, but this boat does not look like a candidate for a v drive, or any inboard style prop shaft at all. The v bottom is too steep and the boat is too big. The prop and shaft will be too low in the water and too far forward to work well. A stern drive places the prop and thrust point about 4 feet farther aft and a foot or more higher. This gives more leverage on the hull to lift it up, plus the trim capability. I do admire your ambition and creativity and would be very interested to see this happen, but this looks like a stern drive deal if you want speed. Two of them really, for maneuverability and total power. Better yet, two big outboards. That would give you any speed you want. Good luck regardless, anyone that can build a boat from scratch has my admiration.
DJ
 

·
Registered
Joined
·
1,640 Posts
Amm, very interesting project you have going. Do you already have the hull. Got any pics? As for HP needed to push the boat into the 70's with the v drive conversion, I think you will need close to 700hp to get a 30 ft vdrive into the mid 70's. There are plenty of sterndrive boats in that range that take 600 or more to get there. Just curious, without the ability to trim the boat, how it will handle? I'm sure tabs can help, but they add drag.



Darrell.
I respectfully change my mind! I gave you the 600 hp based on the 20' estimate in your first email. DMOORE is right. Also your profile in the drawing does not seem consistent with the pics you provided.

You're definately talking outdrive or outboards here. I still think a blown 496 would easily let you cruise in the 70's without being too wild. It's not too difficult to get 700 hp and loads of torque with that setup. You will want trim tabs, and a good prop can make a world of difference.

I suggest you spend some time researching outdrives, props, etc on the offshore forums. Make sure you're sitting down when you check out the prices!
 

·
Banned
Joined
·
1,517 Posts
Mid engine direct drive with a steep angle-that hull will not take a set:D
I would recommend GlenL's book: inboard motor installations
 

·
Amatuer
Joined
·
241 Posts
Discussion Starter · #15 ·
The Glen-L book says that this can be powered by twins & v-drives, plural. V-driven surface drives could be interesting...
There are lots of powering options. I need to make up my mind.

The plans show the surface drives in more of a direct drive fashion. The engines tilted down about 5 degrees and then connecting to a universal joint and then to a surface drive. Surface drives seemed a little too exotic for me.
 

·
Spot On Dee El...
Joined
·
688 Posts
There are lots of powering options. I need to make up my mind.

The plans show the surface drives in more of a direct drive fashion. The engines tilted down about 5 degrees and then connecting to a universal joint and then to a surface drive. Surface drives seemed a little too exotic for me.
About as efficient as it gets though, and v-driven you could overdrive them depending on your power.
 
1 - 17 of 17 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top