Most common used motors

Hey folks. I'm in the early stages of construction on a small powerboat. For budget reasons I'll probably be using a pair of used outboards, at least for the first year. Power will be in the 100 HP range. Since I haven't finished the transom yet, I can modify it

So here's the question. In that range am I more likely to see 20" legs, or 25" legs?

DC

 

If you are looking for a deal on a used outboard, build a transom for 20". You can add an insert for a 25" leg.

 

Thanks Gonzo. I built it at 20”, but the last couple ads I saw were for 25” motors. I worried I was making things harder for myself.

 

If you do get a pair of 25" legs, then you have the distinct advantage of being able to mount the engines 5" higher - and that 5" means a lot really in terms of keeping parts of the motor as far away from or even out of water.
Re the ally powercat in my avatar, we managed to get the engines high enough such that even the zincs on the bottom of the brackets were out of the water when she is in the lightship condition. And still have the propellers immersed deep enough. One reason for this is that the hulls have a lot of rocker. And the engines (2 x 150 hp) thanked us for this.

 

Okay. Then I can move forward from there.

At the moment I'm torturing my poor brain designing the laminated beam that forms the core of the Ram. The forward surface is easy is easy enough. It's just the shape from the offsets. It gets harder as I subtract for deck planking, tunnel planking, and side planking.

 

There is little to no load on the Ram, right?
Accept on impact (collision).
Otherwise, it's simply pressing against a hard point for crew transfer when a dock is not available.
It would be a shame to add lots of Ramming strength and weight when it's not really needed.
Or am I missing something here about the Ram?

 

Regarding OB's and Jack Plates and long legs:

Finding a used pair of counter-rotating OB's may take some time.
I'd start looking now, locally.

I agree, long legs can be nice for higher mounting.
They can be both, more expensive and cheaper, depending.
Wouldn't a pair of extra-longs be fun!

 

I'll start looking now. See what turns up.

The ram will just be a 2*12. Well, built up to that. Need to shape it carefully so that all the planking can land fairly on it.

 

You won't need counter rotation on a boat that is as stiff as a sled. It will sit flat, or to the extent it doesn't, easily tweaked by differential trim, considering the motors will be spaced. 25" is preferred in a 25 foot boat, without a doubt, even though there is plenty of buoyancy aft with this boat.

 

You c

I am confused. Wouldn't you want the zincs in to do their job?

btw, I am also going to jack my engines up on 20" transoms...cost for the jacks is $500@

 

The zincs are only out of the water when she is light, ie not carrying passengers (she carries up to 50 pax on coastal cruises and snorkelling trips).
And the outboard engines are tilted up when she is not in use, so no part of the engine is in contact with the water.
But the zincs are definitely immersed when she is carrying passengers.