I/O or vee drives?

[snapper340]

I am currently in the design phase of building a 29' LOA X 8'6" beam flybridge Sportfisher. what kind of propulsion should I use? the deadrise @ transom will be 18 degrees with a 45 degree entry angle. the finished boat will weigh about 2 tons. the engine will be a Chevy 350 that produces around 360 - 400 hp (SHP not yet known). Any Ideas?

[gonzo]

A sterndrive is more efficient. Vee drives give you more interior space forward than a standard inboard. Sterndrives also draw less than a shaft driven propeller. The structure design is different for each. Sterndrives need a stronger transom. Another consideration is the difference in the center of gravity. It will determine the beam aft. Also, if you need any quotes on prices, let me know.

[BrettM]

Your displacement sounds light, but obviously depends on a lot of things. What contruction material are you planning on?

[snapper340]

I am building the boat with wood frames and plywood decking The weight is just a rough guesstimate. I got the idea for the boat from a GlenL plan(phantom) and I am still a long way from starting the building phase.

[Ward]

What are you doing to the engine to achieve that HP? I have built many car engines (have a SBC 400 in my firebird), and you're gonna need some serious stuff to get that much power.

[gonzo]

I assume you are talking about peak horsepower. A Chevy 350 will not last long producing 400 HP. For intermitent application (25% of the time) 330HP is normal. Remember a continuous duty engine will be about 310 HP. That is the power you can run it and expect a long service life. I think the expense of building an engine with that kind of power is justified only if you want to get a fast hole shot. In a cruiser it won't make much of a difference. The $5-6K difference may be better invested in a genset and AC unit. However, the boat has to please you ultimately.

[ted655]

Another option (better?), is the drive made by DBD. This allows more flexability in engine location. I like it's "plug and play ability. You won't be held hostage to a particular engine.

[gonzo]

Both VolvoPenta and Mercruiser use GM blocks. Chevy engines are the cheapest to hotrod too. I don't understand what do you mean by "getting held hostage to a particular engine". What other configurations can you get with DBD that makes more economic? And what about the cost of the drive itself; and later for parts and service?

[ted655]

With the DBD drive you can buy any engine anywhere you can get a deal. auto salvage, marine salvage want ads. I have an I/O, so I have had dealings with Boat shops. Whew! At least Jessie James used a gun. As for costs, rhere are far fewer parts and they are less expensive than most of the common failures on I/Os. I'm not sure how we would compare the cost of the different drives. Buying from the bellhousing back to the prop, plus all the controls and fittings would be how much for the sterndrive? The DBD total cost is $5,000.00. It's tiller is very simple.
As far as versitility of installation, the DBD wins hands down. You could put the engine in the bow if you wanted and still have stern drive advantage.
So if your Mercedes or Toyota gets smacked in an intersection and your building a boat, you have your engine. I'm not aware of any adapter rings for the bellhousing on a Mercruiser outdrive. That was my point. It's another option to consider.
. http://www.dbdmarine.com/dbdmarine.htm .

[gonzo]

WARNING! Automotive engines are not marine. For starters the electrical systems are not sealed. They are a fire and explosion hazard and also illegal. Also, automotive engines are not rated for the same use as marine. The gaskets are not stainless steel, the pistons will fail at the sustained high RPM's of marine use, the camshaft is designed for a different torque curve, etc. Also, referring to installation in the bow, you are talking of a jack-shaft , which is available through Mercruiser and VolvoPenta. I resent the implication that boat shops rip you off. Marine parts are more expensive to manufacture. They are also produced in less quantities than automotive ones. It is irresponsible to advocate using automotive parts or "any engine anywhere you can get a deal".

[ted655]

In an ideal world, you are of course correct. But here in the real world of less affluent homebuilders we make do. I didn't mean YOU persomaly were a rip off. I can see where the DBD is a threat to some.. Some think it irresponcible for anything to be done outside the establishment of the professionals. Safety is everyones concern. It's implementation shouldn't just be doled out by the elite. It;s really common sence. Sorry I hit a nerve. DBD is a great idea whose time has come.

[gonzo]

I think DBD is a good product. I got some information from them recently. My concern is with using automotive equipment on boats. As a marine surveyor investigating marine accidents, I've seen too many burn and exploded boats. I can assure you it has been an ungrateful task to give an insurance check to a widow or surviving children. The biggest problem is with the fuel and electrical systems. The rest is only a matter of reliability and service life, not a safety issue.

[ted655]

I'm in complete agreement with you.

[RANCHI OTTO]

I find very interesting the DBD propulsion system.
It looks simple, nice and with low resistance if compared to outboard or sterndrive.

RANCHI Otto

[cyclops]

Go out and buy a reconditioned 350 G M marine engine with trans. complete @ a discount price. Do the same for a auto recondition engine and marine trans. Then price out used marine parts to convert the auto to a marine. Post the $$ and where you can get all the parts. You will be almost as old as me and the engine will be as reliable as my reconditioned body.