Differing HP's in tandem on 14' Vhull

[Weirdboymike]

Hey there. Got a question I feel may be a stupid one but never hurts to ask right? I have a 1980 14' Lowe Skipper Vhull that I am thinking about re-powering. I currently run a 1957 7.5 hp (AD-10 I believe) that runs great, though not the fastest thing on the water. Cleanest Smoothest motor ever and got it at an auction for only $30!! anywho... I got a fishing/camping trip coming up and with the other guy, myself, and all the gear I feel I will be under powered. I also have a JW-10 I believe (3hp), also from the 50's that I used to run. I am wondering if I hook them up in tandem how the math works out. Would it essentially be 10hp? What are some of the possible issues with doing this? I am also trying to work a deal to trade the JW-10 and another '50's 3hp motor for a 9.5 or possibly a 15 but the boat is only rated for 10. I did beef up the transom a little though already this spring so thinking it might be ok with the 15. Both 3hp outboards are currently not running so some work would need to be done. Do you think I would get a good deal from a guy who repairs and sells outboards if I offered a trade (currently attempting with a guy)? I would like to keep the 7.5.

 

[Scott Danforth]

what does your capacity tag say for HP? use that as a guide. the specs list 10hp http://boatspecs.iboats.com/Lowe_Boats__14_Skipper__1980/bp/66b117621

no, a 7hp and 3hp wont make 10. the 3 hp wont be providing much if any additional over the 7hp. sell both and get a bigger 10hp motor

 

[jbcurt00]

I suspect the running 3hp will acutally decrease the performance of your 7.5hp....

 

[Weirdboymike]

No Title

Thanks for the input Scott!! I will be attempting to trade the 3 hp motors for one working 9.5, the guys seems interested. Like I said, I would prefer to keep the '57 7hp Johnson (its got a special place in my heart).

 

[fishin98]

Swap the 3's , even throw in the 7.5 for a decent newer 9.5....nothing ruins a fishin trip more than a motor taking a dump on you. Make sure the 9.5 is in good running order before you leave, you won't regret it. When it comes to the motor on the back of the boat, there is NOTHING more special than one that runs.

 

[JimS123]

A tandem would be one in front of the other. But I don't think that would work either.

 

[fhhuber]

Well... assuming you meant side by side for using the small motor sort of as a kicker/booster...
In theory it could work.

You'd impose a turning force by the unbalanced thrust.

As long as the small motor is trying to push the boat faster than its actually going, its not slowing you down. That moves you to calculating peak rpm at the prop vs prop pitch for both motors. If they are close, then you'll be faster with the two, but steering might be a big problem.

If the calculated speeds are off by 20% don't even think about trying. The slow motor will drag like leaving a trolling motor down.

Then we get to the connections needed to link the throttles and steering...

Good luck. Use a lanyard kill that will kill both motors if you attempt it.

Overall I wouldn't try. But if the "pitch speeds" work out and its set up right... it actually might be faster to run the 7 + the 3 than a single 10 hp. It could also be extremely dangerous if done wrong.

It does have the advantage of being unlikely for you to have both engines fail at the same time from anything other than running out of gas.

 

[Weirdboymike]

I ended up getting my hands on a '53 15hp evinrude.almost got it going. The lower cylinder doesn't have spark so i got new coils. However upon removing the flywheel the coils looked new and seemed to be reading correctly. But the condenser lead was rubbing on the flywheel and got down to the copper.hoping that's it. How do you test condensers and how do they go bad?

 

[boobie]

They can go bad from old age and it's takes a special tester to test them correctly.

 

[Weirdboymike]

I just replaced them both as well as both coils, even though I did have spark on the one cylinder. Now I have some spares. Did a full service to this guy and it is purring like a kitten now. Below is a link to the youtube video of it running in a barrel. This is before the fine tuning, and right as I ran out of water so you do hear it slapping. I will get video of it on the lake this weekend. I also have video of my '53 3hp Johnson (prior to fine tuning). I also want to get video of my '57 7.5 hp Johnson (which is my favorite motor right now).