What size outboard should I get?

[stumpwalker]

I have an old 15 foot tri-hull with a 50 HP Johnson circa 1971. There is not label anywhere to be found regarding weight and motor capacities. The motor has a compression issue that is not fixable. My question is what would be the smallest and largest horse power rating that can be used on this boat? I am not really concerned about speed since this boat is used primarly for fishing and the larger the motor the larger the cost. I go from point A to point B fishing spot but do a lot of fishing on Seneca Lake in NY which is a large rough lake. The only concern I have by going to a smaller HP is as it relates to the weight of the boat and stuff that I bring. Gotta pack sandwiches and cold drinks plus I alone weigh 250lbs.

 

[eavega]

Re: What size outboard should I get?

Do you know the manufacturer or any other detail about the boat that can give you a clue about the capacity? I have a 1976 fiberglass tri-hull, and it is rated to a max of 70 HP. I have seen them rated as much as 90, and as little as 40. Since you really don't want to exceed the max HP for the boat, the most obvious suggestion would be to stick with a 50 HP, since that is what is in there now. My tri-hull came with a 1972 50 HP originally, and it was a challenge to get it on plane until I added smart-tabs and lowered the prop pitch. Even then it was a challenge to get on plane heading into the wind. I blew that motor up, and replaced with a 70 HP (the max rated capacity for my boat) and the boat has been much happier since. You definitely don't want to be underpowered especially if you need to go someplace in a hurry (running from weather, for example).

As to bigger HP=more money, I would argue that. At least around here it seems that the more portable small HP motors (up to about 20 HP) are precious and even the "vintage" ones will be listed for about $500-$800, which is the same price range to get the bigger (50 HP - 115 HP) motors.

Rgds

 

[stumpwalker]

Re: What size outboard should I get?

Do you know the manufacturer or any other detail about the boat that can give you a clue about the capacity? I have a 1976 fiberglass tri-hull, and it is rated to a max of 70 HP. I have seen them rated as much as 90, and as little as 40. Since you really don't want to exceed the max HP for the boat, the most obvious suggestion would be to stick with a 50 HP, since that is what is in there now. My tri-hull came with a 1972 50 HP originally, and it was a challenge to get it on plane until I added smart-tabs and lowered the prop pitch. Even then it was a challenge to get on plane heading into the wind. I blew that motor up, and replaced with a 70 HP (the max rated capacity for my boat) and the boat has been much happier since. You definitely don't want to be underpowered especially if you need to go someplace in a hurry (running from weather, for example).

As to bigger HP=more money, I would argue that. At least around here it seems that the more portable small HP motors (up to about 20 HP) are precious and even the "vintage" ones will be listed for about $500-$800, which is the same price range to get the bigger (50 HP - 115 HP) motors.

Rgds

I attached a picture. Your pictured boat is very similar. I have done much work on the boat (too much? LOL) and there is no label with name of manufacturer and such. There is a 70hp Mercury listed locally and I was toying with the idea but your comment about sticking to a 50hp has merit.

 

[spoilsofwar]

Re: What size outboard should I get?

FWIW, my (now sold) '72 starcraft 15 foot trihull was rated for up to 85hp, and I had an old 1970 merc 800 (80hp) mounted on there. Different hull then yours, but still, I highly doubt a 70hp will be too much for it.

 

[NYBo]

Re: What size outboard should I get?

Welcome to iboats!

Is the a HIN (hull identification number) anywhere on the transom? If it's a '71 it won't have a standard number, though, and we may not be able figure out much from it.

 

[UncleWillie]

Re: What size outboard should I get?

The 50hp vs. 70hp argument can be decided by asking the boat!
Did it seem happy and sufficiently powered with the 50?
Were you constantly running at WOT?
Or did is seem like it could use a little more scoot?

If it did seem well powered with the 50; Going to a 70 is not going to suddenly turn it into a rocket.
Even if it does, there is no reason you could not just back it down a little!
The engine will last much longer if you run it at 75%.

I remember there was that one guy that used to complain that his boat had too much horsepower...
But, he was the same guy that complained that the boat was too big, and he had too much money!

 

[aerobat]

Re: What size outboard should I get?

I have an old 15 foot tri-hull with a 50 HP Johnson circa 1971.

The only concern I have by going to a smaller HP is as it relates to the weight of the boat and stuff that I bring. Gotta pack sandwiches and cold drinks plus I alone weigh 250lbs.

well, you alone 250 lbs with the suitable amount of sandwitches to keep the mass may in a 15footer basicly look like this :

http://pidge2571.files.wordpress.com/2010/04/fat-man-boat.jpg?w=630

so be aware the bigger engine brings in most cases more additional weight on the transom and your poor small 15footer should stay floatable on good days

 

[southkogs]

Re: What size outboard should I get?

I don't think there would be a weight concern between a 50 and a 75 (I've actually had both in Evinrude and they were pretty similar) on your boat. It's possible that 50 would be the top stop on your boat - I've seen several 15' boats like that. How did it plane with the 50HP? I had a rather heavy 15' boat that didn't like running on the 50 (I had it on while I worked on the 70), but if yours planes out with the 50 with a couple of people on board, you may want to stay at that HP.

That said, more likely the max HP is between 65 and 100 - in which case I don't think you'd overpower too much (if at all) with a 75HP.

 

[Home Cookin']

Re: What size outboard should I get?

I'd go with 48-55 but I'd grab a good deal up to 70--the mid-80's OMC 70 is a great motor, as was the 55.

since you cross big water, being underpowered would be dangerous.

 

[stumpwalker]

Re: What size outboard should I get?

The transom is solid but if I went up to a say 70 hp I have seen boats with a metal plate attached to the transom, would something like that be needed? As for planing, last summer I was on Great Sacandaga Lake on vacation. I had the 1971 50 hp Johnson on it which has 140 compression on one clylinder and 80 compression on the other (that is why I am replacing) and I could not make over 10mph or so with 3 skinny people and one fat me. I had it almost wide open and I did not push it either considering the compression issue.

 

[aerobat]

Re: What size outboard should I get?

I had the 1971 50 hp Johnson on it which has 140 compression on one clylinder and 80 compression on the other (that is why I am replacing) and I could not make over 10mph or so with 3 skinny people and one fat me. I had it almost wide open and I did not push it either considering the compression issue.

well, with 4 adults where one is you on heavy weight its nothing suprising that a 50hp may struggle to get the boat on full plane. when the boat is small and "overloaded" with the 4 persons you may also have a very stern heavy mass distributaion and end up with a high bow , low stern and pushing the boat against the waves without getting the a..s out the water for planing.

running 4 adults calls for something bigger than 15foot and of course a bigger engine.

 

[ezmobee]

Re: What size outboard should I get?

The transom is solid but if I went up to a say 70 hp I have seen boats with a metal plate attached to the transom, would something like that be needed? As for planing, last summer I was on Great Sacandaga Lake on vacation. I had the 1971 50 hp Johnson on it which has 140 compression on one clylinder and 80 compression on the other (that is why I am replacing) and I could not make over 10mph or so with 3 skinny people and one fat me. I had it almost wide open and I did not push it either considering the compression issue.

If your transom is solid, it should be able to properly support up the rated horsepower of the boat. That being said, I did add one of these to my boat when I mounted the motor (despite having a brand new transom) because basically.....why not?

http://www.basspro.com/Transom-Support-Plate/product/22508/106964

http://i176.photobucket.com/albums/w200/ezmobee/New Boat/DSCF2640.jpg