aquasport 246cc diesel tunnel drive

[gon2sea]

hi everyone, im new to the aquasport world... just started a project on my 246CC, installing a cummins 6bt and tunnel drive...
going v drive as even a bravo II doesnt do well behind the cummins due to the low rpm and torque.
i have already done this conversion twice on larger uniflites, a 27 express and on the 28 mega i still have...
here is a link to some pictures, keep in mind the project is only 3 weeks old..!
https://picasaweb.google.com/1049052607 ... sport246Cc

[Aswaff400]

seems like overkill for a 24 ft boat. and thats coming from someone who wants to put a 383 stroker in a 200 osprey.    

we have a few yanmar powered boats at work, they are running the larger bravo one X/XR drives and bravo 3 XR. the bearings, gears and shafts are much stouter than the standard bravo one or 3

cant wait to see what kind of performance the boat has when its done!

[gran398]

Welcome aboard!

Interesting conversion, looking forward to seeing how she turns out.

Your method of tank removal falls in the category of "why didn't I think of that?"

Fill the coffin with water....and the tank floats out

[gon2sea]

it would of been much easier to simply bolt on an outdrive but so far the volvos and mercruisers  are not built to hold up behind the 6bt, even the bravo II X Diesel isnt up to the task, the yanmars are smaller and higher revving engines and dont have the low end grunt of the cummins.... and besides at some point this boat will live in the water in the sea of cortez and outdrives, even though they tolerate sea water, dont hold up like a good shaft and prop.
Overkill would of been spending $25,000 on a new cummins marine 370 hp engine, this will end up being 1/3 rd the price of a new 200 hp outboard, will get close to twice the fuel economy and will last 15,000 hrs and the boat was free.... and i have 5 other cummins... what else was i supposed to do..!

[Capt. Bob]

Oh my,
A rather unique installation. Very interesting.

Good luck and keep posting pics.

[dburr]

Overkill would of been spending $25,000 on a new cummins marine 370 hp engine, this will end up being 1/3 rd the price of a new 200 hp outboard, will get close to twice the fuel economy and will last 15,000 hrs and the boat was free.... and i have 5 other cummins... what else was i supposed to do..!

Raise a toast to King Neptune and all those that have gone before good sir and post some pictures! Going to be a cool project..

Curious, what kind of speed are you looking for? My interest is in shaft angle and wheel size for the tunnel..  Might give a surface drive or water jet a thought if you want 20+ and skinny water..  She is gonna sound COOL!!!!!

[gran398]

it would of been much easier to simply bolt on an outdrive but so far the volvos and mercruisers  are not built to hold up behind the 6bt, even the bravo II X Diesel isnt up to the task, the yanmars are smaller and higher revving engines and dont have the low end grunt of the cummins.... and besides at some point this boat will live in the water in the sea of cortez and outdrives, even though they tolerate sea water, dont hold up like a good shaft and prop.
Overkill would of been spending $25,000 on a new cummins marine 370 hp engine, this will end up being 1/3 rd the price of a new 200 hp outboard, will get close to twice the fuel economy and will last 15,000 hrs and the boat was free.... and i have 5 other cummins... what else was i supposed to do..!

Here's the good news. The weight is slightly behind midships, low in the hull...exactly where you want it.

[saltfly]

I like the idea. As for  structural integrity. I think it will be stronger enough. I think you will tie the motor mounts into the stringers their by spreading out the motor weight and the tunnel its self will add to the structural integrity of the hull. It will be like adding a large rib. This will be interesting to watch. I do have a question. With the motor, drive and tunnel, where will the fuel tank go and how large will the tank be?

[Capt. Bob]

this boat was designed for about 475 lbs to be hung on the transom not 1500 lbs in the middle of the boat, Originally the boat was designed for about 1000lbs Motor and fuel. Your going to be over that with no fuel.

Well in 75, the 22-2 was built to handle both outboard and inboard applications. Weight difference between the two was listed at about 800lbs. on the inboard side. I would guess that increase was due to the motor which was placed amidships. Different length hull but design-wise probably not a lot different than the 246. Just a guess.

http://www.classicaquasport.com/gallery ... oa&cat=557

A little bit on the layout.
http://www.classicaquasport.com/gallery ... hp?cat=558

I believe you're working with this hull with the CC cap.
http://www.classicaquasport.com/gallery ... 0s&cat=546

Good luck.

[gran398]

I like the idea. As for  structural integrity. I think it will be stronger enough. I think you will tie the motor mounts into the stringers their by spreading out the motor weight and the tunnel its self will add to the structural integrity of the hull. It will be like adding a large rib. This will be interesting to watch. I do have a question. With the motor, drive and tunnel, where will the fuel tank go and how large will the tank be?

Saddle tanks may be worth considering. Another idea may be to transversely mount a tank in front of the engine across the stringers in a coffin. Regular shape tank in front of the engine....she may be a digger in a following sea.

[gran398]

This is an Albemarle 24, same hull as the old Formula 24 or Prowler 24.


The inboard engine is beneath the console, jackshaft drive.


Just called Albemarle....the boat runs twin tanks, outboard of the stringers, 60 gallons each, slightly aft of amidships.

[gon2sea]

the motor weights in at 1200lbs including transmission etc.... the cummins marine 6bt uses cast iron for manifold and other pieces... the bowman manifold is alluminum, also the placement of the engine, as cpt bob mentionned is more midship balancing the weight out, both my uniflites, weight in at 8500 lbs and will do 20 knots at 2600 rpm with same engine, i have no doubt she will do 28 to 32.
think of it this way.. add four adults and you've added 600 to 800 lbs... the motor weight really is not a concern, spreading the weight with strong engine beds is important.
regarding fuel tanks i have room left forward of the engine in the original tank recess for a 60 gallon tank... plenty for 8 hrs at cruise. im starting out with a 18X26 prop, should put me in the ballpark of where i want to be. Eric

[wingtime]

18 x 26 prop?  Wow that is a big wheel. I guess gobs of torque is the key there. What is the gearing on the transmission?

[gran398]

What do you calculate as running weight, no passengers, full fuel?

[gon2sea]

lets see.... 2550 boat, 1300 motor , ruder , shaft etc... 500 fuel, 500 passengers, thats 4850.
the shamrock 246 with gasoline weighs in at 4300 dry with gas engine, throw in the optional yanmar 6lia  and its well over my figure...  im not looking for a speed demon, just a good solid and sea worthy hull, hopefully i'll get a chance to take her out before heading down to baja in late september, but i have no problems taking her and doing sea trials down there....