aquasport 246cc diesel tunnel drive

[seabob4]

Yes CB, just like any standard tranny, you have what we call "down angles".  Trannies are available in a number of different down angles.  Builders design the hull bottom, particularly the shaft log portion, to utilize what's available, down angle wise.

Eric said his Hurth was a 12 degree, which IS a little steep.  He'll jack up the front end of the motor, which will reduce that angle in relation to the hull.  Do his rear engine beds properly, he'll be fine...

[saltfly]

Man this thread is really getting cool. So many different things involved that are different then normally done here.  

[gon2sea]

in this application, like on most larger boats, the vdrive is bolted solid to the engine and the shaft uses a standard shaft coupling / flange to transmit power, the prop shaft goes thru the vdrive hollow shaft allowing the coupling to be accessible on the back side of the transmission instead of under the engine / transmission. as such standard marine mounts are used as they have to take the forward thrust and keep alignment.
the picture posted of a Vdrive speed boat is using a CASALE vdrive, most of those are actually over geared, where the prop spins faster than the engine.
i will be using twin exhaust, i will Y right off the turbo and run down thru each muffler.
https://picasaweb.google.com/1049052607 ... 3665832786

[RickK]

Stringers look pretty beefy now  

[seabob4]

Eric, not really sure why you want to Y the exhaust, other than for symetry purposes.  Single exhaust and 1 muffler ought to do the trick.  Line the engine box with Soundown, and you'll have your quiet boat.

One of the biggest challenges with inboard installs is the exhaust routing, especially on small boats.  Big boats with lots of below decks space, not that big of a deal.  But exhaust hose is BIG, as the wall thickness is typically about 3/8", so even 4 1/2" hose comes out to almost 5 1/2" DIA, which takes up a LOT of room.  Then you have to make room for the muffler.  Eric, I'm very curious as to how you plan to route...

[gon2sea]

turbo diesels, and i suspect most turbo applications DONT like back pressure, if the exhaust isnt free the turbo wont spool up..., cummins recommends a minimum of 5" exhaust on their 300hp 6bt. i know from past experience that i had to increase exhaust size 3 times on my first cummins install, of course in hindsight i should of simply measured exhaust backpressure.. being a mechanic, it always felt like something was holding the engine back untill i went with a 4" (sch10 pipe -4-5/8" od ) off the turbo and after 2 feet split into two sch10 3" ( 3-5/8" ) and out thru the transom, what a difference that made, night and day. i had a bunch of sch 10 stainless from a job we did at a large semiconductor plant upgrade in the DI / RO plant. sadly im short on that but have some 4" stainless tube that will work for the exhaust and matches the two mufflers i have and im sure i will get a bit of back pressure from the mufflers.
So, that is my train of thought, proof again that bigger is better....lol..
the " engine bay" is pretty cramped so i will route the exhaust just like i have the mufflers laid out in the picture and straight out the back. it will require a stepped engine cover but that isnt a problem.
got most of the tunnel "mold" done today, will finish tomorrow after work and start glassing so hopefully by next week end i'll be working on the stuffing box and the prop shaft strut.
Eric

[gon2sea]

added a few pictures of the tunnel fiber-glassing progress....
https://picasaweb.google.com/1049052607 ... 4155071154
running into town today to get 12ft of 3 X1/2 stainless flat bar stock to make the shaft strut and "cage " to protect prop.

[Capt. Bob]

The tank location sounds interesting. Please take some photos before dropping the motor back down.

Thanks.

[gran398]

[dburr]

Really nice progress!!    

What's the plan for a stuffing box? And the wheel guard, are you planning on a shoe made with the flat bar?

[gon2sea]

the tank location is the front third of the original tank as the motor doesnt take all the room in the old tank " recess " under the floor. finished fiberglassing the tunnel today, will probably work on the rudder tomorrow, unlike my other tunnel boats where the rudder has a bottom bearing, this one will be supported by the tunnel and a upper bearing on a bracket bolted to the inside of the transom, this will minimize on drag under water., made a 2" fiberglass tube today for the prop shaft / stuffing box, will have to re- mount the motor to align it and glass it in.
the prop cage will be slightly different as well compared to my other boats, it will be single instead of double, again to reduce drag

[Tx49]

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..!

Sell one to me for a third the price of an O/B?

Seriously, I love the sound of this build. Oh wait, I was serious about the other too.

[dirtwheelsfl]

Have any p-pump motors laying around?  

[gran398]

Eric,

Wasn't that long ago the good members posted my pics. And I really appreciated it. Now it is my turn.

Photo Gallery had issues loading up tonight.....one pic at the time unfortunately

First cut, tunnel drive install

[gran398]