Barrelback w/ Mercruiser 3.0 or 4.3 and zf hurth or velvet drive?

[carl_shipwright]

Hi, I am new here and a shipwright from Sydney.

Soon I will be undertaking building a 17' Chris Craft barrelback replica - cold moulded in marine ply. I am wondering how difficult it is to fit a normal inboard transmission to a Mercruiser 3.0 4cyl or 4.3 v6, which are only available in sterndrive form? I would think it is just a different bellhousing and maybe risers right, but I am not sure if these engines will have the correct bolt patterns. Just thought I would put it to the experts here as picking which engine to use is one of the first steps I am taking.

I think that the 135 hp of the 3.0 should give the small boat enough power for 30mph or so, but I might go for the 4.3 (190hp) from which I would expect 40mph. Any prop and transmission ratio reccomendations for these engines?

Thanks
Carl
Carl Rickards Classic Boats/Sydney Harbour Boatbuilders

[SplineWeights]

Use a Volvo-Penta. They are easier to setup for inboard use due to the mounting system. You will need a 14" flywheel and a SAE 4 or 3 (cant remember which) bellhousing. The transmission should be a 1:1 ratio. Go with the ZF over the Borg Warner types. The ZF is lighter.

[mongo75]

Or you can just use a "Chevy" small block. It don't make a difference who slaps a brand name on it. You can always find inboard mounts for a small block Chevy on ebay or any online store for pretty cheap, vice buying a Merc or a Volvo marinized engine.

[carl_shipwright]

The reason I want to go with a new mercruiser is because of the availability of the engine on ebay from the states cheaply due to the usd being low, parts and dealer support in Australia. I don't want to get into marinising a chev because by the time you add up buying an engine and the required parts and labour (I could do it but would rather spend my time working on someone elses boat to cover the cost of it), it is cheaper and easier to buy a brand new merc with warranty and no stress factor.

Regardless, I have now decided to completely redesign the shape of the hull below the waterline so that it will have a v-drive and will most likely be 19-20 feet long. This shape will need either the 4.3l 6 or I may go for the inboard-designed 5.0 v8 carb engine. Has anyone here fitted a v-drive to these before?

[Jango]

Be carefull with Bottom design, although at 40 MPH it is less critical.
An Excellant Design for either In-line or Vee Drive:

http://www.glen-l.com/weblettr/weble...94.html#monaco

I chose to go with inline because of the Classic Looks, but could have gone Vee Drive with a Central Double Cockpit. Either would have worked since CG would be similar.

Good Luck, Jango

[SplineWeights]

If the boat is now longer than 20' (and if the CG and displacement supports it... etc) I would go with the 5.0. Besides the 5.0 mercruisers can come inboard complete with tranny from the factory

[Jango]

Just remember, the faster you want to go, the more important CG becomes.
Try to install your inline motor as far aft as practical.
Good luck with your project

Jango

[TollyWally]

"Or you can just use a "Chevy" small block. It don't make a difference who slaps a brand name on it"

LOL except...Mercruiser exhaust risers are a wee bit thin and the Swedes are just too proud of thier parts. Crusader makes about the best engineered "Chevy" in my opinion.

Personal Disclosure, I am the proud owner of a big block chevy marinized by our Swedish friends. Good solid engineering but the parts are too damn expensive. Also you need a set of metric wrenches to fit the swedish parts and a standard set for the american ones. My .02

[Eric Sponberg]

Carl,

My Cherubini Classic 20 is just such a design:

http://www.sponbergyachtdesign.com/CC20.htm

http://www.cherubiniyachts.com/20.html

We started with a 200 HP Mercury Jet, and have upped that to a 220 HP Yanmar diesel with I/O drive. One of the options we have considered, and if they get an order for development it will move ahead, is to have a 4.3 liter gas engine, 225 hp at 4400 RPM, with a Walter V-drive, with 1.46:1 reduction, propeller 15" x 22". The reason we would choose a V-drive is because of the current tooling for the deck and cockpits necessarily places the engine aft. It is too expensive at this point to change the tooling for a little more room in the engine compartment. As it is, the V-drive gear is under the rear seat in the after cockpit.

In the diesel configuration, the boat runs like a champ. The Yanmar verified performance report with 220 HP in-line 6, 183 cu.in displ, Mercruiser Bravo 1 outdrive, gear ratio 1.50:1, prop 14.125" x 21" 3-blade Mercury Enertia, gives a boat speed of 47.50 mph at 4071 rpm. Boat weight is about 3,000 lbs.

Earlier this year I completed a new set of construction patterns for a 21' Chris Craft Cobra reconstruction project in which the owner wanted a new deep-V bottom and convex sections forward, instead of the original flat bottom with concave sections forward. This project is almost done, and the boat will likely be in the Mount Dora Classic Boat Show in March '08. The owner is fitting a 350 HP Pleasurecraft 6.0 liter Crusader gasoline engine. The gear will likely be the ZF 63 IV at 1.294:1 reduction, going to a 14" x 17" Michigan Wheel, 3-blade DJX prop. The shaft angle is 10 deg. to the bottom hull at centerline, which is basically horizontal to the flotation waterline. With this bottom configuration, we expect the performance to be as sweet as the CC20, and faster to boot.

I hope this gives some guidance.

Eric

[Jango]

Looks like a real nice Design Eric.

I have a Question: How does the Boat go 13.62% Faster than a 21 Pitch Prop can produce at 2714 RPM (4071/1.5)? With Slip, should be much Slower?

[Jango]

Correction: My Mistake, you're actually getting exactly 12% Slip, if Prop is exactly 21P.