14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

[Dillpickle]

I just got a 14 foot Sears fiberglass tri hull fishing boat and I put my 1958 Johnson 10hp seahorse on it and off to the lake I went with my fishin buddy.

Here is the problem...boat will not even come close to planing...it plows heavy in the front. I adjusted the trim at all positions and it worked best at the higher positions, but it was just plowing the whole time.

I had a set of those plastic flaps on the cavitation rails and I am thinking maybe they need to come off and try again?

This Seahorse motor has all kinds of power and runs like a scalded dog....no issues whatsoever with the motor....just acts like its pushing a big old log through the water...

can i even expect this motor to plane this boat with two guys...500lbs and all our fishing gear?

Thanks for ya'alls help and advice in advance.

 

[MH Hawker]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

I sort of doubt it has enough power to move it onto plan. Glass boats are heavy to start out.

 

[spoilsofwar]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

No way a 10hp is enough to plane a 14 foot fiberglass boat with two guys and gear aboard... You're gonna need double that, probably more.

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

It's a 20 hp limit on this lake we fish ... Will a 20 do it?

 

[spoilsofwar]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

It's a 20 hp limit on this lake we fish ... Will a 20 do it?

I dont know... It would certainly do better with 20hp then the 10hp, but whether it will plane or not I couldn't say without more info. How about some more details about the boat? Or pictures, we love pictures

 

[bonz_d]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

If it's the same model 14' Gamefisher that I'm aware of they are not that big, wide or heavy as some may think. Is there a capacity plate located somewhere in the boat?

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

If it's the same model 14' Gamefisher that I'm aware of they are not that big, wide or heavy as some may think. Is there a capacity plate located somewhere in the boat?

I will have to look but at first look, I didnt see one.

 

[kfa4303]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

You may also need to raise the motor a few inches to get the anti-vent plate to be level, or slightly higher than the keel. OMC motors of this era had sort of an odd leg length of around 18", which makes them too short to be a modern 20" "longshaft", but too long to be a modern "Shortshaft". As a result, you often have to build a transom rise, or jackplate to get the motor to the best height. Simply clamping the motor as high as possible on the transom can help too, but you usually end up needing a few more inches. I recently built a transom riser for my '66 20 hp and it has helped quite a bit. Make sure you're not carrying any excess weight either. Here are some handy links.

http://www.leeroysramblings.com/johnson_QD.htm

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

Thanks You all for the great information. I appreciate your help.

 

[Home Cookin']

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

I agree that a well-running 10 should work for the old gamefisher-type boat, which is a lightweight shell hull with no insert, not a "heavy fiberglass boat" like a bayliner or something.

However 2 250# men and their beer--I mean, gear--is too much weight to zip off on a plane with a 10 hp.

The adjustment to make is not with the motor but with your friends. Start by moving him back; if that doesn't work, move him to the dock and take his sister instead. Seriously, though, you trim small boats by moving stuff around, and perhaps the motor tilt rod. You can get a boat obn a plane by running over shallow water, too, but you have to know your bottom (works over mud not rocks)

Try running it alone and see what happens.

A 20 would work, maybe even a 15 would be enough--can you borrow any motors to see?

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

I am going to try it without the cavitation plate. Then I am going to take it out alone and see if it will do better. It does have added weight with a front deck, and seats and a battery up front as well so this may all be a case of weight distribution....I am looking for a 15 or 18 or even a 20hp Johnson Seahorse that I can rebuild and get ready for next season. I do enjoy the older motors, so thats my plan at the moment. I will try to post a picture of the boat soon.

 

[bonz_d]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

Nice little boat by the picture!

At this point I really think a newer 15hp would be a better choice than an older 18hp as I believe the 15 is quite a bit lighter overall and I would trade the extra 3hp to reduce weight. Also you haven't stated as to whether you found a capacity plate. Another option would be to check out the prop. I do beieve they used to make 3 different size props for that motor and as a rule a bigger diameter with a flater pitch helps with heavier loads.

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!




Here is a data plate that I found for it.

 

[bonz_d]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

So there you have it! Max hp is 20 and max capacity is 760# for all passengers, engine and gear. So if you have 2 people at 400# that leaves just 360# for engine, fuel, battery, cooler, seats, all tackle and whatever misc. stuff you need.

At this point I would compere the weights of your 10hp to that of an 80s 15hp to that of the 18/20hp engines and use that to decide which way to go. I still think a late 70s thru 80s 15hp would be the way to go as I think it has the best weight to hp ratio and would be a nice step up from the 10hp.

 

[Dillpickle]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

You may also need to raise the motor a few inches to get the anti-vent plate to be level, or slightly higher than the keel. OMC motors of this era had sort of an odd leg length of around 18", which makes them too short to be a modern 20" "longshaft", but too long to be a modern "Shortshaft". As a result, you often have to build a transom rise, or jackplate to get the motor to the best height. Simply clamping the motor as high as possible on the transom can help too, but you usually end up needing a few more inches. I recently built a transom riser for my '66 20 hp and it has helped quite a bit. Make sure you're not carrying any excess weight either. Here are some handy links.




http://www.leeroysramblings.com/johnson_QD.htm

View attachment 160092View attachment 160093View attachment 160094View attachment 160095View attachment 160096

i looked at the cavitation plate height in comparison to the bottom of the hull and it actually sits about and inch and a half below the lowest point of the bottom of the transom/hull. Is that little of a distance enough to make a difference in this situation? I am also considering going with th 8 1/2 prop to see if that will help out as well. I would guess that fully loaded we are moving about 6 to 7 mph at WOT.

 

[kfa4303]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

Hi Dill. A difference of 1/4" can make a noticeable difference in some instances. Any inch and half is more than enough to cause excess drag. You should also notice better/lighter handling by raising the motor a bit. As you can see, I also use a tiller extender which lets me shift my weight forward and/or stand while underway. All of these factors together add up to improve overall performance and handling. I would try to get the anti-vent plate level with the keel, testing it, then trying a new prop if need be. There are all sorts of jack plate/risers out there. I just made mine out of materials I had on hand. I agree that your at about the max for that little 10 hp, but you might be able to squeeze a bit more out of it by adjusting the height, trim/tilt, weight distribution within the boat.

 

[Home Cookin']

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

I am going to try it without the cavitation plate. Then I am going to take it out alone and see if it will do better. It does have added weight with a front deck, and seats and a battery up front as well so this may all be a case of weight distribution....I am looking for a 15 or 18 or even a 20hp Johnson Seahorse that I can rebuild and get ready for next season. I do enjoy the older motors, so thats my plan at the moment. I will try to post a picture of the boat soon.

View attachment 160237

well now that we have pictures, it's a different story. I was picturing the gamefisher that is a single hull (got one) but yours is the equivalent of the 13' whaler--much heavier and much better.


I grew up with the same boat, but a whaler, and an 18. Now have a 20 on it. Where I sailed, they used the same with 9.9's for tenders and they would do ok with one person, no gear, but barely.

All that stuff on the bow is killing you. I hope you don't run it with someone sitting in the high chair up front.

A 25 is a great motor for that boat but 18-33 will do. 15 is too small; 9.9 too small. Forget cavitation plates, etc. just get the right motor. Probably a short shaft

 

[bonz_d]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

A 25 is a great motor for that boat but 18-33 will do. 15 is too small; 9.9 too small. Forget cavitation plates, etc. just get the right motor. Probably a short shaft

How can you reccommend a 25hp or larger when the capacity plate clearly states 20hp max?

 

[Home Cookin']

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

How can you reccommend a 25hp or larger when the capacity plate clearly states 20hp max?

you're right; I missed the post about the plate. Keep it in the limits.

I think you can go higher with a console.

I see that the plate is not the manufacturer's but the state; didn't know they issued them. That may explain the lower HP limit.

 

[bonz_d]

Re: 14 Ft Sears Trihull and a 10Hp Johnson 1958 seahorse...help!

Thought it was just an oversight but I still needed to point it out before some one did something foolish.