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Outboard HP ratings

3K views 19 replies 10 participants last post by  204Angler 
#1 ·
Hey again.
16' Lowe big jon max hp rating is 35. With the amount of weight I've added mid-ship and forward that '81 Johnson 35 is not impressive at all. It was never a fast boat and I've never expected it to be however, it's to the point where with one other person on the boat the hole shot is dismal and top end is not amazing. It's down right annoying.
That being said I know a heavy 16', beamy aluminum with modifications adding weight, two batteries etc... It won't ever be a speed demon and I don't want/expect that. I have two different props, compression is good on both cyl's etc. I've got plenty of freeboard as well. It just seems like my 14' Polarkraft (used to own) with a hyper 25 evinrude on it with identical mods would absolutely smoke this boat.
my question is if I found a 40hp would you guys be nervous about hanging that on the back? And I'll mention also that the transom is solid. I believe the weight difference is about 40#'s
I know I'll get words of caution which I get and won't bash but I'm just really curious if any of you have done this or know of anyone who has and what were the results.
 
#3 ·
You may want to try a pontoon prop. Your power to weight ratio is not great, and a pontoon prop should get you on plane easier, but you may lose some top end speed.

The pontoon prop should essentially give you more torque to get on plane than a regular prop. The prop will have much fuller more rounded tips than a normal prop, even with the same pitch.

Fishscalz
 
#6 ·
Any idea where your RPMs are at? If proped correctly you should be turning close to the max RPMs with your average load. Top much pitch and you may not be turning enough RPMs, too little and you are essentially spinning your wheels. Another thing to think about may be mounting height and trim angle if it doesnt have power trim.

I also agree that insurance company may frown upon exceeding the recommended horsepower, that could hurt you at resale time too.
 
#7 ·
Yeah..... I'll probably leave it alone after reading what y'all said. I'd like to try a pontoon prop, never thought of that and honestly was ignorant to the fact that they existed....or, different anyways.
So I will try my lower pitch prop. I still have to get one of those cheap "bolt on" tachs so I know what it's turning. One thing with the 15P is its lugging with someone else on the boat. Also a peculiar problem: when I hit choppy water or waves, the prop starts the ventilate and rpms increase dramatically. It's a 15" transom and shaft so am unable to lower the motor and if I trim motor down (no power t/t) one more hole, the boat plows. At that point obviously handling is all but diminished.

Ill play with it some but do you think a mini dolphin tail would help the ventilation? If I stop and start again it's ok. When it does that I can look back (tiller steer) and see the "waterline" is below anti ventilation plate....

Thanks guys.
 
#9 ·
Well I'm tracking what you're saying,and when I tilt it one hole up, it gets outta the hole quick but still blows out. I have everything but trolling motor battery in the stern. For kicks (and I trust you) I'll place some ballast made up of my gf on the bench beside me to see if that helps. It's almost as though if I had a tunnel it would be perfect
 
#10 ·
I had a Sea Nymph FM161 with a 1989 Johnson 50 HP tiller and then added a CMC PT130 and it ran like a scalded dog! The boat came with a 25 HP Merc and was slow if there was any load in it.
As a disclaimer, you do what you want to do and it is your choice.
Do you even have insurance on it?
 
#11 ·
No insurance now since whole boat/motor/trailer MIGHT be worth 2k but I do want to get insurance on it. I cancelled insurance on my big boat (not using it).
I'll play with the props/motor position/weight but if that don't do it I may borrow my buddies 50 just to see freeboard and performance gains. From there make a call on a 40 or trying a known healthy 35. Maybe my motor isn't healthy. Seems like a 35 ought to do better.

i know it's not a performance boat by any stretch but.... It's really doggy
 
#14 ·
you might ask Lowes if they can re-rate the boat for a little more horsepower. I've seen my own 17.5-foot aluminum model rerated from 50 to 70 max hp when another owner requested it. I'm happy with my 50, but the higher rating is there if I ever want it. When you talk to your insurance guy, ask him about liability as well as equipment replacement.
 
#15 ·
I didn't know you could do that, good info!

i spoke with someone with a hull almost identical to mine, it's a polarkraft but same semi V, 16' x beam etc and he gets a good home shot and 30 mph with a 35, 15P prop. I'm going to check compression on my motor....
 
#17 ·
I suggest changing the plugs with what the MFG says. Check and clean all the contacts. Spraying cleaner in the carbs really does nothing for the carbs. If you have gas issues you need to rebuild the carbs.

Does that thing have a rubber bushing in the prop? That could be hard also.

mike
 
#19 ·
i have replaced the plugs and rebuilt the carb. Fuel pump was good as well as bulb/all fuel lines. One thing I did notice is the butterfly valve is not opening all the way. It is a linkage issue I've attempted to fix but keeps slipping back. It's a lock screw on the rod that opens carb and goes to stator. It keeps slipping back to original position. Butterfly valve probable not opening all the way by 10-15*.
No rubber bushing. Like I said I've got two props, one 13P the other 15P. 15P is in great shape, bought new about 3 months ago.

I will do as you suggested and clean all contacts, double check gap on plugs and being one carb... Too easy to remove and double check it as well.
 
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