Dangers of over-powering?

[hibbert6]

I have a 15' tri-hull with a 650 merc. It does OK, though it's hard to get a less-than-talented slalom skier up. WOT is about 32mph.

The hull is rated for 80hp.

I have a shot at buying a Merc 950 for cheap. If I hung it on the back of my boat, just what would I be risking? Might I "torque-off" my transom? Would it be so heavy as to drag the stern? Might it make me go too fast for safety?

Thanks!

Dave

 

[SpinnerBait_Nut]

Re: Dangers of over-powering?

IMO, it's never wise to go over what the CG plate says your boat is rated for.
With that said, I have seen it done several times with no ill effects.
You can/could be in trouble if you ever were involved in an accident and was discovered to have a engine that was past the rated HP for your boat.
JMTCW.

 

[pduquette]

Re: Dangers of over-powering?

Hi Dave +SBN
Just to pick your brain SBN , (no legal ramifications implied) My old '61 boat has no plate . I've already determined From a '59 sales catalog for the similar modle craft was 50 hp . But if I use the boat building/powering formular I obtained on another site ( I think it was a USCG formular) my max safe hp should be 65 hp. would you think me a fool to squeak the "extra hp" on my transom ? or since there is no defined max hp can I safely go with the formula . And ...when was the change from powerhead hp rating changed to prop hp ; and how would this affect my decision?
thanks Peter

 

[SgtMaj]

Re: Dangers of over-powering?

Peter,
The biggest danger in overpowering with outboards, is having the motor jump in the boat with you. That being said, it's the same danger as having a rotting transom. So if your transom is in excellent condition, then the difference between 50 and 65 hp isn't going to pose a serious hazard in my opinion.

SgtMaj

 

[tashasdaddy]

Re: Dangers of over-powering?

as long as you have a splash well, sudden stops, can sink boats.

 

[SpinnerBait_Nut]

Re: Dangers of over-powering?

Peter, check your transom good and make sure it's solid as SgtMaj says.
If it is then you should have no problem with the 65.
Weight wise, they should be real close.
If the stearn sits low in the water, like TD says, watch them sudden stops.
Don't take much water over the stearn to cause problems.

 

[Lakester]

Re: Dangers of over-powering?

hello,

the Lakester Special is a 15.5 tri-hull. rated 80HP. has been running 85HP for past 35+ years. i wouldn't hesitate to put on 100, 115 or even 125! she will run upwards of 40 knots.

you wont be using the rated hp unless u run it at the rpm it is rated at to produce that hp. for me it is 5,000 rpms on my evinrude. and how u apply the torque at low end will have more affect than how u use the hp at a higher speed, well, i mean aisde from hitting things...

regards,

lakester

 

[Silvertip]

Re: Dangers of over-powering?

You realize there are legal ramifications involved which you didn't ask for but I'll bring it up anyway. If you have an incident on the water, whether your fault or not, the legal system will be all over you like stink on a skunk -- especially if personal injury involved. If you happen to live where it is not illegal to overpower a boat this is probably not an issue. If you go ahead with your plan, at least change the decals on the motor to at least "deflect" law enforcement and the legal beagles.

 

[Texasmark]

Re: Dangers of over-powering?

One problem I have always had with this rating thing is how engines are rated. Since the prop power is what puts the the boat in motion and is the stress twisting on the transom, one would think that if he were using a pre-prop rated engine, that there would be allowances for that.

My insurance co has a couple of spaces on the policy that mean a lot to insurability and cost of the policy: What is the HP rating of the boat; what size engine is on the boat. My boat is rated for 130 and has a 90 on it. Good numbers for cheap insurance. If you are over the rating you don't have to worry about what it costs; you don't get a policy!

Back in the days of the OMC "Fat 60" (the first 60 hp 4 cyl in the '60's) a friend built his own wooden boat. First time out he hammered the throttle and ripped his transom out. Must have missed a calculation somewhere.

Mark

 

[pduquette]

Re: Dangers of over-powering?

Morning Silver tip + all .
I posted my questions more for edification purpose than toget permission to bust some laws. Like many others here I got my old boat as a project, all ripped apart . no data plate to speak of. I rebuilt the transom, have a splash well roughed up (still need to finish). I'm rebuilding a J50 so I doubt the extra 15hp will be a great jump in speed for me to justify another motor swap.
I'm more curious to when Hp ratings changed and how that affects dataplate listings : and in lieu of a data plate, how would the USCG rate my boat transom/ hp rating if boarded for a "curtosey inspection"

 

[DJ]

Re: Dangers of over-powering?

hello,

the Lakester Special is a 15.5 tri-hull. rated 80HP. has been running 85HP for past 35+ years. i wouldn't hesitate to put on 100, 115 or even 125! she will run upwards of 40 knots.

you wont be using the rated hp unless u run it at the rpm it is rated at to produce that hp. for me it is 5,000 rpms on my evinrude. and how u apply the torque at low end will have more affect than how u use the hp at a higher speed, well, i mean aisde from hitting things...

regards,

lakester

BE CAREFUL.

There are several things to consider:

1. Your 65 is really about a 55. Engines before 1983 were powerhead rated, not prop rated.

2. I strongly supect the integrity of a transom of that age. I may be wrong, it may be rock solid. That is your first priority, check the integrity of the transom.

3. The USCG and the Water 5.0 isn't going to care what was said here. They will check the plate and your engine. Citations may follow.

With all that said, a "modern" 75 would really wake that hull up, if the transom is solid.

 

[guy74]

Re: Dangers of over-powering?

BE CAREFUL.

There are several things to consider:

1. Your 65 is really about a 55. Engines before 1983 were powerhead rated, not prop rated.

2. I strongly supect the integrity of a transom of that age. I may be wrong, it may be rock solid. That is your first priority, check the integrity of the transom.

3. The USCG and the Water 5.0 isn't going to care what was said here. They will check the plate and your engine. Citations may follow.

With all that said, a "modern" 75 would really wake that hull up, if the transom is solid.

I have a couple questions about this.
1. If my boat was rated for 85hp in 1973 would it be a no-no to put a modern 85hp motor on it.

2. Also if my boat never had a data plate, it's too old, how would the "Water 5.0 know if it was overpowered.

3. Does anyone know "firsthand" of anyone getting into legal trouble with an overpowered boat. I've never heard of anyone getting in trouble around here with an overpowered boat, and I would guess that 1 in 4 of the boats on our local lake are overpowered.

I guess the best statment I've heard about it is "Overpower at your own risk"

 

[Silvertip]

Re: Dangers of over-powering?

As for data plates, HP is HP regardless when it was determined so IF you have a data plate and you are overpowered I would expect a ticket would be issued. If there is no data plate -- as in an old boat -- I would guess there is nothing legally they can do but I would suspect they will inspect the boat verrrrry carefully looking for any weakness as an excuse to get you off the water. At any rate, they would not likely question the size of the engine unless they saw, for example, a 150 haning on a light 14 footer. These people are not stupid and have a pretty fair idea what is acceptable and what might be "over the top". Again, your insurance dude might have something to say about it as well. But then if there is no insurance, we are back to the original "incident issue". Yea I know -- I'm preaching so I'll get out of here.

 

[DJ]

Re: Dangers of over-powering?

I have a couple questions about this.
1. If my boat was rated for 85hp in 1973 would it be a no-no to put a modern 85hp motor on it.


2. Also if my boat never had a data plate, it's too old, how would the "Water 5.0 know if it was overpowered.

3. Does anyone know "firsthand" of anyone getting into legal trouble with an overpowered boat. I've never heard of anyone getting in trouble around here with an overpowered boat, and I would guess that 1 in 4 of the boats on our local lake are overpowered.

I guess the best statment I've heard about it is "Overpower at your own risk"

1. Legally-No. If the transom is solid, go for it.

2. It's up to you to prove it isn't. If they "think" it is, they'll issue a citation.

3. I have. It was an issue as described in #2. What a mess. Only the USCG formulas proved it wasn't. However, the burden of proof was on the owner.

 

[ztim]

Re: Dangers of over-powering?

DJ was talking about the motor when he said "Engines before 1983 were power head rated, not prop rated."

So, my 78 6hp is really what?

Also, my boat does not have an ID plate. I think it because it was rebuilt. It looks like an old Sears 12' semi-V hull.

 

[DJ]

Re: Dangers of over-powering?

DJ was talking about the motor when he said "Engines before 1983 were power head rated, not prop rated."

So, my 78 6hp is really what?

Also, my boat does not have an ID plate. I think it because it was rebuilt. It looks like an old Sears 12' semi-V hull.

Correct, I was talking about the engine.

Not ALL engines automatically lost HP when the rating method changed. The general rule was to get engine makers to rate their engines truthfully within 10%, either way. Some engines, in the past, were also underrated.

The '6' maybe a 6 or it may be a 5 or it may be a 7. Who knows. Impossible to tell without a dyno.

Without a plate, you are kind of on your own. I don't think anyone is going to hassle you if you have a 9.9 or less.

 

[SgtMaj]

Re: Dangers of over-powering?

Another thing if excessively overpowered, is that the transom might develop stress cracks and allow water in to rot out the transom over time.

 

[Texasmark]

Re: Dangers of over-powering?

I agree on the dyno only knows, and agree that the CG could use the hp rating tables to measure your boat and determine the numbers if no plate exists. I have also known of people putting different cowlings on their engines with lower hp numbers and getting away with it. Course if you swapped cowlings and had a bad accident, the ins co., looking for a way out probably would detect it and you would be the sorrier for it.

You know, rated hp is just a design objective and some companies just underrated their engines...like old Mercs and Martins to name a couple. Also, you could take a production run of 100 engines and would probably come out with all meeting the min but for those which had everything right, they could be 10 to 15% high.

Also, is the rpm thing. Since an engine is stated to develop it's "rated" hp at a certain rpm, running 10% higher in rpm's "could" net you 10% additional hosses.

So, it's pretty subjective and probably your level of rapport with the CG inspector probably has more to do with how you fare.

My 2c,

Mark