Giving up on outdrive, going diesel v drive, need some help.

[clctrader]

Ok guys, I asked about Volvo and bravoIII outdrives not long ago to use with my Perkins but am just gona save some headaches and $. I will go V drive with my project.

Heres the deal:

I have a 26' with a 10' beam Proline project boat. I Installed a Perkins Range4 275ti under the center console. The engine has 275hp and lots lots lots of torque. Top RPM is 2800.

What kind of transmission and gear ratio do you guys think i should use to achive top speed with the v drive setup? What prop size should i start trying with?

I am new to marine diesels and am lost in V drive configuarions so any help will be greatly appreciated.

Thanks

[Scot B25]

Lots of options here, a friend just did a 315 hp 6BTA into a 25 Bertram. He went with a ZF 220V drive set up in 1.5:1 ration, 22 x 23 4 blade. The boat is excellent, cruise is around 26-27kts...WOT is about 32kts.

Check out the boatdiesel.com site and I suggest you pay the $25 bucks and join the site. Lot's of information about V-drive diesels on that site.

I believe you will end up with a 1.5:1 gear and something like a 19 or 20 x 22 or 23 wheel. But I don't know your WOT and cruise rpm's on that Perkins. Use the prop calculator on the site to determine ratio and wheel size. Should get you in the ball park.

I am installing a Detroit 6V71N 287hp into a 25 Bertram, but mine is in-line with a small pocket. Mine requires a 1.12:1...because the Detroits are low-rpm diesels and I need the shaft rpms.

Based on my experience you need to have the prop-shaft spinning between 1400-1900 rpm for a decent cruise speed. Anythink in that range can be adjusted with the prop to maximize effeciency.

Do yourself a favor and check out the site....best $25 bucks you will ever spend.

Good luck.

[boatdiver]

I don't think you will be able to use a v-drive under the console. You'll want to go with with a straight shaft set up so you don't end up with an extremely long shaft with a bad angle. My advice at this point would be to find a local reputable shop/refit yard and advice. If you are to figure the cost of a trans, v-drive, shaft, and strut, you'll be very near the cost of a jack shaft and outdrive setup. I still think the best solution is to go with a jack shaft and Volvo outdrive. I think if you figure the cost of a drive assembly and jackshaft you won't be that far away from any other setup and it will be the best solution. You won't need a transmission with an outdrive and the boat will end up being faster and most likely more efficient.

I think it would be a shame to try and save a couple of bucks at this point and end up with an inferior finished product.

[Scot B25]

end up with an inferior finished product

That statement could (and is) be debated for hours on end. If he plans on leaving the boat in the water ANY inboard configuration is superior, hands down. What he is considering will not be as fast or as shallow water versitile as an OB....but will certainly out live any outdrive and is a much stronger drive train.

As far as dependability, it's not even a contest. Show me an out drive behind a diesel with 10,000+ hours?...there are plenty of diesel inboards out there with these hours.

Wether V-drive or in-line depends on the hulls COB (center of bouyancy) and "where" the engine needs to locate to keep the hull trimmed correctly. I'm not sure about the Prolines, on the 25 x 10 Bertrams the bare hull COB is 10ft forward of the stern cap.

It boils down to how he wants to use the boat.

[Scot B25]

I suggest you log onto the Carolina Classics owners wedsite. This is a very good representation of a bunch of guy's that have jack-shaft diesel outdrive boats and guy's who own the exact same boat with inboards. Ask those owners which way to go.

[marsea]

Try giving Walters a call. They make one bulletproof trans. They are super nice guys.
If you give them basic dimensions they can help.

http://www.waltergear.com/

[clctrader]

Wow, I have a headache. I will do some further reasearch with the info you guys have provided me with. I really appreciate it. I have a friend thats a marine diesel mechanic and he sugested that for reliablility, shaft is the way to go. I will take a break and get some more info before i bust out the grinder to the boat.

Thanks again to all of you, god bless and have a great weekend

[Aliboy]

Shaft should be superior from a reliability and maintenance point of view. Possibly better resale as well. Downside is slightly reduced performance and possibly manoeverability.
One thing you will need to do at the beginning of the excercise is work out where the prop and rudder will be located. The prop diameter will be limited by the clearance required between the prop tips and the hull bottom (I seem to remember that the rule of thumb is minimum clearance of 1/3rd of the prop diameter - check this). The combination of 'clearance', ideal prop diameter, and prop placement allow you to work out the required shaft angle and also shaft strength (combination of shaft diameter and material used). Note that for good performance and gear ratio calculations, you should first work out what the ideal prop diameter is. Whilst you can alter the performance by playing with the prop pitch, you can not indefinitely increase the pitch to make up for lack of prop diameter.

[glacierbaze]

My idea of a vee drive is a motor installed backwards in the rear of the boat, with the shaft running forward to a coupler/tranny, and another shaft running back from there to the prop. You say that you have installed the Perkins under the CC. Which way is it facing?

[Scot B25]

The standard acceptable tip clearance on an inboard is 10% the diameter of the prop. Personally I like just a bit more (11%-12%) for piece of mind.

A "remote" V drive may place the engine extremely aft and uses a torque tube to connect engine to V-drive. Thus the term remote, because....the V drive element is remote from the engine.

Most V drives use an integrated marine transmission/V drive that's built into a single gear. This can locate the engine more amidship than aft.

Yes...the engine faces aft.

[billinstuart]

I like inboards, but I would NEVER make that kind of change to that hull. First, youve gotta add stringers, then pad the hull for both strut support and rudder. In any case your draft will substantially increase because the prop is way below the bottom of the hull. And all the alignment problems.

Why not just jackshaft drive an outdrive and be done with it?

[Doug in Bermuda]

Sorry I can't give you my specs but my sig boat has a single Cummins 6BTA 315hp with a -F (dead keyboard key) V drive. The hull is deep. With it's full hollow keel I need almost 4' water but the prop is almost 90deg to water surface. Shaft angle is insignificant.

There is a similar hulled CC boat here with what must be the same Perkins block. This one is an early 90s 6-354, 240hp. Don't know his tranny setup but the CC appears set fairly far fwd which suggests it may be a straight shaft drive.

[Seacat FL]

billinstuart - 7/9/2007 8:20 AM

I like inboards, but I would NEVER make that kind of change to that hull. First, youve gotta add stringers, then pad the hull for both strut support and rudder. In any case your draft will substantially increase because the prop is way below the bottom of the hull. And all the alignment problems.

Why not just jackshaft drive an outdrive and be done with it?

billinstuart is exactly right. That boat was not built to be an IB. You might could make an IB out of it but is it worth the trouble?

Be simpler to do an outdrive or buy an old IB boat that needs repowering.