Motor size?

[JCNailen]

I was hoping to find this in the engine FAQ sticky's, but didn't. I need a motor for my 19' CC. It's a project, so it doesn't have a plate with recommended HP size. If I recall, there used to be a formula based on LOA x Beam x something, something, something?

The P.O. said it had a 70hp on it. Found a sweet deal on C.L. for a 80. Should I go higher?

 

[trendsetter240]

Re: Motor size?

I was hoping to find this in the engine FAQ sticky's, but didn't. I need a motor for my 19' CC. It's a project, so it doesn't have a plate with recommended HP size. If I recall, there used to be a formula based on LOA x Beam x something, something, something?

The P.O. said it had a 70hp on it. Found a sweet deal on C.L. for a 80. Should I go higher?

The USCG formula is (length x width x 2) - 90. I would think you'd be doing just fine with a johnson/evinrude v4 90-115.

 

[82mustang]

Re: Motor size?

That cannot be the formula, I've got a 14' tinny, no floors, just 2 bench seats and a split rear bench, and that formula would mean that i use a 50hp if i round the beam down, and a 78 if I round up my beam measurement. The capacity plate says 30, and thats what I have on it, and trust me, a 50 would be insanity. Or is that formula for glass boats, not tinnys???

 

[jasonbailey]

Re: Motor size?

Must be for glass boats. I have a 18 Foot tri-hull glass boat with a 6 foot beam.

18X6X2-90=126 Then to be happy minimum should be .70 or so of the 126 which equates to 88.2. My rig has a 90 on it and it pushes it with a full load about 37MPH. I'd say it's pretty close.

 

[CATransplant]

Re: Motor size?

It's also base on how the boat is controlled. A tiller boat will have a lower horsepower rating than a boat with remote steering.

 

[trendsetter240]

Re: Motor size?

It's also base on how the boat is controlled. A tiller boat will have a lower horsepower rating than a boat with remote steering.

Yes that is the forumula for remote steering, 20" transom boats. Alum. and fiberglass.

 

[trendsetter240]

Re: Motor size?

That cannot be the formula, I've got a 14' tinny, no floors, just 2 bench seats and a split rear bench, and that formula would mean that i use a 50hp if i round the beam down, and a 78 if I round up my beam measurement. The capacity plate says 30, and thats what I have on it, and trust me, a 50 would be insanity. Or is that formula for glass boats, not tinnys???

It is in fact the USCG forumula, feel free to look it up. There are other considerations involving control and handling tests but that formula is the basic rule.

You do not round the numbers. If for example your beam is 54" then in feet that would be 4.5. Does your boat have a 20" transom and remote steering? I should have added that stipulation. 15" transom boats with tiller steering can not use that forumula.

 

[JCNailen]

Re: Motor size?

Is this the "suggested" or the "Max"?