Need help With Motor Size

[spence88]

Hello, I hope I'm posting this in the correct place. I recently got an old 70's Ouachita 1432 flat bottom Jon Boat from my father. I had a new transom welded on the boat and a few other spots repaired at the same time. In hindsight, I should've just bought another boat. But here I am. My question has to do with what motor to put on this boat. I?ve seen where people have older 15hp omc?s on 1432 Jon Boats. But I got one hell of a deal on a 1972 18hp Evinrude. From what I?ve read the 15 and 18 horse motors are about 10 to 15 pound difference in weight. I don?t know the exact weight of either.

I think Torque would be the biggest difference.

What?s the difference in weight compared to a 9.9/15 to an 18. 10 to 15 pounds, I believe

I?m not sure and I?m new to boating. So I?m turning to you guys in hope that you can shed some light on this for me.

Would it be safe to run the 18 or should I go down in HP?

 

[hardwater fisherman]

On the outboard manufacturer pages here at IBOATS they list a 1972 18hp short shaft at 81 lbs and long shaft at 83 lbs. The older motors for the most part where lighter then modern ones. I dont know which year 9.9/15 hp you are looking at but they seem to be any where from 72lbs up to 84 lbs. What is the hp rating for the boat?

 

[spence88]

I do not know the HP rating of the boat. The tag was long gone when I got it.

 

[spence88]

The guy that welded the boat did a great job on the transom. I have two 3/4 inch pieces of marine grade plywood glued together for the transom. That I haven't installed yet.

 

[hardwater fisherman]

My guess would be 15hp but it could be less.

 

[Scott Danforth]

that transom looks narrow. could be rated for 10hp or less

 

[hardwater fisherman]

Yes I did not see the photos before I posted. The transom is quite narrow. Probably as you say 10hp or less.

 

[Sea Rider]

Don't know about Evis, on other OB brands 9.9-15-18 HP weights near same. If your case, you can always limit the internal throttle mechanism to perform as a 10 HP if wanting to. Could add a wooden piece on internal transom to make it thicker.

Happy Boating

 

[spence88]

Don't know about Evis, on other OB brands 9.9-15-18 HP weights near same. If your case, you can always limit the internal throttle mechanism to perform as a 10 HP if wanting to. Could add a wooden piece on internal transom to make it thicker.

Happy Boating

That was my dilemma was how close the 9.9/15-18 are in weight. Within 10 pounds of each other. Once i paint the boat (weather permit) and install the transom, I plan on replacing the brace from the floor to the transom for added support.

The boat is narrow 32 inches on the floor. I've found people putting 15hp on boats with the same specs online.

I'm going to run my current setup nice and easy to see how it goes.

I'll be sure to post my results.

 

[Scott Danforth]

Use the US coast guard formula

http://newboatbuilders.com/pages/hp.html

0.5 x (14x3.5) -15 = 9.5hp

 

[jbcurt00]

Thats using a 42in transom width across the top of the transom.

Might be even rated lower if the transom is closer to 36in across the top.

 

[Scott Danforth]

exactly a 14' long boat with a 3' wide transom would be rated at 6hp

a 12' long boat with a 3' wide transom would not be rated as it would be a row boat only

 

[mickjetblue]

No Title

Another model, same 1432 size boat, has a max of 7hp.

 

[Ike-110722]

It is very easy to calculate the rated horsepower. You only need to know the boat centerline length, the maximum transom width (widest part including rub rails), the transom height, and whether you have remote steering or tiller steering. See this page.. http://newboatbuilders.com/pages/hp.html