Max HP?

[gnarbrah]

I recently bought a 1979 Johnsen Skiff to match my little 6hp outboard. It works well but not near enough get up and go so I'm really looking at getting into a 15 hp. The boat is registered as 12' but actually its 11' with a tape measure.

Anyone know if there's a registry that documents these things? (The coast guard plate is MIA)

Thanks!

 

[tashasdaddy]

Re: Max HP?

http://forums.iboats.com/showthread.php?t=191283

 

[CATransplant]

Re: Max HP?

When I first read "Johnsen skiff," I thought it was a misspelling. Apparently not. Does it look like this one?

If so, it looks to be a seaworthy sort of craft. However, I'm betting that the plate would have said something around 10hp. A 9.9 would probably be ideal. 15 might be a bit much on a boat shorter than 12'.

 

[gnarbrah]

Re: Max HP?

CAT-
You are correct not a misspelling. It looks somewhat different than that one, mine has an enclosed bow, only 2 benches. One in the back and one midway with a little hatch for cooler or baitwell. Its a neat little set up. The 4 rivets are still in the back where the Coast Guard plate used to be. I was thinking 9.9 until I read all the info about how the 9.9 and 15 (Johnson) are basically the same motor weight and physical size. You just get an extra third more horsepower with the 15.

Am I correct in thinking this?

I'll put some pics up tonight of it to give you a better idea of what I'm working with.

Thanks for the input!

 

[CATransplant]

Re: Max HP?

I tried really hard to find a hp limit for that boat, but there's very little info on the web about Johnsen boats.

The 9.9 and 15hp Johnsons and Evinrudes made since the late 60s are identical in weight...almost identical in other ways, too.

The only worry I'd have with the 15 is a safety concern. If you run those little skiffs too fast, they can be tough to control, and it's easy to turn too quickly at speed. But...I don't know what the max rating is on the boat, so I'm just guessing. Fiberglass boats are heavier than the equivalent aluminum boat, like the 12' one I have. It's rated for 10 hp as the max.

It planes with the 6hp outboard and does about 15 mph. With a 9.9, I'd expect 20 mph, and that's faster than I'd want to go in my boat, especially using tiller steering. It's easy enough to jink a little too hard, even with the 6 hp.

Here's an idea? Do you know someone who'd let you borrow a 9.9 for a test? I'm betting that would give you all the performance you can handle.

I saw your other thread, where you're considering a 15hp from the 1950s. I'm not certain, but I think that's a bit heavier than the later 9.9 and 15 hp outboards. For a tiller boat, that can be important.

What does the boat do with 6hp? Does it plane or just plow? I moved some weight around in mine, getting the trolling motor battery and fuel tank up front, and that really helped. Sitting on the back seat is a real issue with small tiller boats.

If it's possible, I'd try a couple of motors on your boat, even if you have to beg someone to let you. Buy 'em a beer or something.

 

[JB]

Re: Max HP?

The 1956 FD-10 15HP is an entirely different engine than the much later 9.9/15 that shared the same block.

Talk about it being "basically the same engine " as a 9.9 is wholly incorrect.

I doubt that your little skiff is rated for more than about 10HP, and I wouldn't put more than 10 on it.

 

[gnarbrah]

Re: Max HP?

I agree, not a whole lot of info out there that I can find either for the Johnsen's. I'll definitely post some pics tonight.

With my 6 it plows unless I'm by myself in the middle seat with a tiller extension. Then it moves pretty good. Problem is, Im rarely alone in it and 2 of my buddies have 12 and 14 foot aluminum boats but both have 15 hp's. I don't know anyone with a 9.9. I can borrow a 15 but I already know what it'll do, go fast. I definitely see your concern about the safety issue but I'm little passed my "go as fast as I can all the time" so I think I'd be able to control it (not to mention keep up with the rest of the pack). We actually do little tournaments and booze cruises pretty regularly and its not a lot of fun watching the literally do circles around me.

Anyway, you mentioned seeing my other post, I also have a few in the Johnson repair forum if you want to take a look. Right now the 6 is acting funny and I actually put a video up from last weekend (its the one where the video is sideways) just in case you might know whats making her run weird.

Thanks, I'm off to take a few pics!

 

[CATransplant]

Re: Max HP?

Well, that's about right, if it planes with you in the middle seat. You could probably adjust the weight balance by moving heavy gear up front. Basically, you're saying that it performs about the same as my 6hp on my 12 aluminum boat. Mine planes, but I've taken steps to balance the weight.

I'd be willing to bet that your boat originally had a maximum hp of 10. That's pretty standard for 12' skiffs. 15 would be 50% more powerful, and that's a lot. I wouldn't do it.

As for "booze cruises," I won't say anything at all. If you're drinking and boating, then overpowering your boat isn't a good idea at all. In fact, drinking and boating is a very bad idea.

 

[gnarbrah]

Re: Max HP?

Don't get the wrong idea, my booze cruises usually consist of 2 beers and a 6 pack of water for all day in the sun. I've seen too many problems by mixing alcohol and boating, especially for the captain.

I'm really starting to question the 9.9 vs. 15 - I just got off ebay seeing what was out there. Basically I just want the boat to plane out with 2 of us in the boat and make it across the lake in a reasonable amount of time. I spend most of my time on chains of at least 5 lakes in the area and its nice to get around and see what there is to see, not to mention checking my favorite fishing spots which are scattered about.

Here's some pics of the skiff. Once again I just want it to plane out well with 2 in the boat. Thanks again for all your advice!

 

[tashasdaddy]

Re: Max HP?

when you have another person with you move the tilt pin out, change the angle of the motor, so the foot is farther away from the transom, this should pick up the bow.