Pros and Cons of OverPowering a Boat

[DavidA]

Situation: I have a 12' HiLaker that I really enjoy. I don't need anything bigger. I'm not small, 5'10" ~ 220lbs. This makes the boat back heavy, even though the gas tank is up front. I have an older (2 stroke) 15 HP Evinrude, that just won't plane the boat. Maybe its the motor, maybe not. The boat is rated for a 20 HP motor.

I have considered buying:
- another 15 HP, 2 stroke, because weight of a 4 stroke is excessive
- a 2o HP 2 stroke
- or, it was suggested, and I am leaning to, get a 25 HP Yamaha, oil injected, which, while higher than the rating, is actually safer if used properly, because it weighs less (~110 lbs vs. 125 lbs for a 20 hHP).

I would like to hear what people think of these 3 options, keeping in mind that money is an issue. Thank you.

[hewesbob]

At a recent NWFR get together at Lake Chelan one of the sponsors (propeller shop from Spokane) put on a great presentation, I always knew that putting a different prop on a boat could change performance but there are other tricks to consider also like at what height your motor is mounted on you boat. To low of a motor could cause a lot of drag thus cutting down on your speed and ability to come up on plane, to high you could cavitate and not realize your power . Just a thought

[Larry3215]

Seems to me a 15 hp should be way more than enough to plane a 12ft boat. It could be several things - wrong prop or wrong trim settings or installation or just a very weak motor.

The main reason not to over power any boat is safety. The Coast Guard and the mfg set those limits because that the max safe HP for that size boat.

[G-Man]

If your Evinrude is running properly, I'd bet the pitch of the prop is your problem, not a lack of horsepower. If you want to go with a new motor, look at the 20hp Suzuki outboards. They are light weight (108lbs for electric start LS) and are now all electronic fuel injected. The electric start units also maintain the manual rope pull starting equipment, so you don't need a battery and don't need to manually wrap the starter cord around the flywheel. The other option I'd look at is a Tohatsu. A little heavier than the Suzuki, but they make such a great unit, other manufacturers have them re-branded to sell as their own.

[BentRod]

Those Highlakers are a bit on the heavy side being fiberglass, right? However, I agree that a properly setup
15-20hp outboard shouldn't have a problem getting it up on plane. Aside from the prop pitch, I've always liked the added performance a hydrofoil fun adds. My brother added a doel-fin to his 15hp 2-stroke Evinrude and it pops his 14' aluminum up on plane in a heartbeat. And that's with two heavy occupants.

PS- a 15hp 2-stoke should be lighter weight (~75 lbs) than the 20-25hp equivalent. Just a thought.

[Mike Carey]

Granted, my boat is not the same as a 12 foot boat, but changing the prop and raising the motor made a huge difference to the tune of 3-4+ mph top end and faster out of the hole.

It could be a weight adjustment would help. Can you add a tiller extender and sit farther forward?

[hewesfisher]

My best friend had a 14 foot Hi-Laker when we were in HS. Nice boat but powered with a 20hp Merc and we fished that boat from the sound to just about every lake in the Tacoma area and beyond. Never a problem getting on plane with both of us.

I had a 14' Hewescraft open fisherman (aluminum) and it would plane with 2 people, small cooler, 3gal fuel tank, transom mounted electric trolling motor, 12v battery, tackle and powered with a 15hp Merc 2-stroke would top out at 23 - 25mph (paddle wheel speed) WOT.

One problem I had with that boat was getting on plane with just me. Same issue you describe, not enough weight forward. Two people on plane instantly at WOT.

Being the Hi-Laker is a fiberglass boat it's heavier than a comparable aluminum boat. More hp might help, but you'll still need to move weight forward for best performance. I don't advise ever exceeding manufacturer's max rated hp.

You don't really have a lot of options when it comes to prop choices on the smaller engines like yours. The 15hp I had wore a 9" x 9p 3-blade prop and was probably the best all around choice. If you think your prop may be damaged, have a reputable shop look at it. A new 9x9 is under $100, so keep that in mind when visiting a prop shop.

If your prop checks out, make sure your engine is in proper tune for peak performance. Beyond than, best bang for buck would be to upgrade to a 20hp.

Modern 4-strokes are light, here are weights for current production 20hp, manual start, short shaft:

Tohatsu 115lbs
Suzuki 97lbs
Mercury 115lbs
Honda 114lbs
Yamaha 111

[DavidA]

Thank you all for taking the time to consider this and provide input.

As far as shaft length, I understand that the short shaft I have is appropriate for this boat. My friend has a long shaft (more drag) 15 HP, of the same make on essentially the same boat and with us both in his, we go 16-18 mph. In mine it is more like 8-10 mph. I have shifted my 6 gallon gas tank up front and have 4 containers of sand up there as well to keep the nose down and this helps. I think any additional weight would likely not improve the situation.

As far as props, mine does have some damage. The guy at the shop where I take it for maintenance has suggested a new one should help but doesn't think it would make the sort of difference I think I should get (+8 - 10 mph). I don't think my prop pitch is 9 x 9, but I will have to check. He did just tune the engine in December, so I'm trusting that is not an issue.

I had no idea that the newer 4 strokes had come such a long way to reducing weight and would like to go that route, but I expect the cost would be prohibitive for me right now.

It sounds like there isn't much support for upping my motor all the way to a Yamaha 25 HP 2 stroke (~110 lbs).
And also, considering some prop damage, maybe not the best prop pitch but proper shaft length, it sounds like this motor likely just isn't up to it.
Assuming my assessment above is correct, and a better working 15 HP should do the trick (probably), do I chance another used 15 HP 2 stroke (~75 lbs) or look for the more power/more weight, 20 HP?

(From what I understand, the Yamaha 25 HP weighs about the same as a 20 HP of most other models)

Again, thanks for all the time and thought to help me out here.

[Sideburns]

On the extreme side of the equation, I have a buddy with a 40hp on a 14ft jon boat. I wont ride in it with him anymore...

My 15ft grumman v bottom boat does mid 20's with 2 adults and gear. Its a 15hp 2 stroke evinrude, so I do have to watch my weight. It pushes close to 30mph with one man and no gear. Any faster than that in such a light weight boat would be kinda scary, but it would be nice to have a little more payload I guess.

I spent quite a bit of time getting the gps speed, weight of the boat, measuring max rpm etc.. to get the prop set-up properly. My prop is a cheap solas aluminum prop, I can get you the numbers if needed.

[Larry3215]

Sideburns brings up a good point - you should seriously consider doing some tests and measurements to see exactly how well your boat/motor/prop combo is performing. It wont do you much good to take them individually because everything works together as a system.

There are two key things you need to be able to measure accurately - RPM and GPS speed. You can get the speed close enough from your cell phone, but you need a way to get an accurate RPM measurement while running at full throttle on the water.

The ideal prop will allow the motor to reach its max rpm at full throttle - not over and not much under. I dont know what year your is, but Im guessing the max rpm is in the 6000 range more or less, so you want that motor to reach close to that value at full throttle.

Just because a motor is tuned up does not mean it is performing as well as it should.

Lets say you find its getting to 5500 rpm and the max is 6000. Thats a little low but in the ball park. If that happens, then you need more power or you need to look closer at the install or load distribution, etc, but you will know the motor is working as it should. You can tweek things a bit with a new or different pitch prop, but it wont make a lot of difference if your close to the max rpm.

However, lets say your rpm are going all the way to or over the max rating at less than full throttle. In that case, you need more prop. Either larger diameter or more pitch or both.

Third possibility is you find the motor is not getting close enough to the max rpm. That could be due to a damaged prop or too much pitch or the motor is just too old, worn out etc. Assuming the motor is basically in good shape, a new prop with possibly a different pitch may well fix you up.

I would buy or borrow a good quality tach and do that test, then let us know what you find. A little testing is a lot cheaper than a new motor and it shoudl also give you an idea of you need to look for another 15 or 20 horse motor.

[Larry3215]

I almost forgot the reason for the GPS speed. Once you have the rpm and speed you can calculate the prop slip value for the boat.

A propeller with a given pitch turning at a certain rpm has a theoretical "prop speed" through the water. A prop with a 9" pitch should move 9" forward for every revolution. So at 1000 rpm the boat should move 9000 inches forward every minute or about 8.5 mph. No boat ever goes at the calculated "prop speed" due to drag, but it should get close - the closer the better.

Once you have the rpm, speed and look up your motors lower gear box ratio, you can use a website like this one to calculate your prop slip. There are a bunch of different ones out there.

http://www.mercuryracing.com/prop-slip-calculator/

[Sideburns]

http://www.ebay.com/itm/122413679539

cheap rpm gauge for just about anything with a spark plug 9 bucks!

[dutchman2858]

Here's an obvious (but free!) thing to check...make sure your motor is trimmed ALL the way down. Anything less than all the way down will result in higher bow and less chance to get on plane.

[hewesfisher]

Many older 2-strokes had lower WOT rpm in the 5000 - 5500 range. To help, we need to know year of engine so you know what rpm your engine should reach. Guessing isn't going to help.

One thing to keep in mind, your buddies boat isn't essentially the same as yours unless it is also a Hi-Laker, same year, same length, same engine, and same weight. It might be worth your while to weigh your boat, loaded how you normally use it, so you know for sure.

Testing with a damaged prop is a waste of time IMO.

Get a tach like Sideburns posted cheap, simple, and effective. It will help immensely. You'll need some way to measure GPS speed. Those two, plus a known good prop and known weight of your boat will be the best foundation to begin testing.

[Bodofish]

Biggest thing about putting a bigger OB than it's rated for is insurance and liability ( AKA safety and reason the Coast Guard put the recommendation on the placard). So injure someone, damage some property, be in any sort of accident and you are hosed. That said, a lot of people put any motor on any boat case in point, every Sat afternoon racer on the lake. They have a lot of fun until they get in sort of altercation...........

[Bodofish]

Many older 2-strokes had lower WOT rpm in the 5000 - 5500 range. To help, we need to know year of engine so you know what rpm your engine should reach. Guessing isn't going to help.

One thing to keep in mind, your buddies boat isn't essentially the same as yours unless it is also a Hi-Laker, same year, same length, same engine, and same weight. It might be worth your while to weigh your boat, loaded how you normally use it, so you know for sure.

Testing with a damaged prop is a waste of time IMO.

Get a tach like Sideburns posted cheap, simple, and effective. It will help immensely. You'll need some way to measure GPS speed. Those two, plus a known good prop and known weight of your boat will be the best foundation to begin testing.

I have to agree 100% , the prop on our little bay boat got bashed on the RR tracks. Almost invisible damage, you really had to look hard to see any. The boat would not plane at all and before it ran 18mph on flat water.
So yeah, research what prop is supposed to be on the motor and get the stock prop and give it a go. Many folks that use a motor of a kicker on a big boat will put a flatter prop on push it hard but not fast.

[TrackerPro16]

It is amazing how much of a difference dinged up prop edges make! Clean them up or replace them and see how much better it is.

[DavidA]

I have been quiet lately but have been watching, appreciatively. I have ordered one of those tach's and will test as suggested. I think the prop I have is 9 1/2 x 10, which I believe is the stock prop, and dings have been smoothed out, but maybe it is no longer a 9 1/2 having been 'fixed' often. My fishfinder does have GPS, and mileages I have discussed have been based on that. Please stay tuned and I will report my findings once my online purchase arrives and I get a chance to test drive it. Continued thanks. Dave