Over Powering Boats

landlockedpirate

landlockedpirate

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Theres been lots of discussion on here about putting more outboard power on boats than they were originally designed for. In general the feeling is that its ok, as long as the helm is experienced and the installation is done well. Back in the 80's my dad always slightly overpowered the family Fletcher ski boats so that they could be used for barefooting and some fairly fast mono sking.

But when does it become dangerous? Boats appear on Ebay from time to time that look stupidly over the top. These boats are usually old, with possible transom degradation or damage and the cheap prices mean they could be bought by newbies with no experience.

Heres an example, very little info, but I think its a Fletcher 129 that had a max engine size of 40hp when new. I would have happily put a 50hp on it but 100hp !



http://cgi.ebay.co.uk/fletcher-100h...tem&pt=LH_DefaultDomain_3&hash=item335f6b843c

Death trap, or just a bit of fun ?
 
I would have thought there are two parts to the equation.

1) How much weight you can hang off the back

2) How much thrust the transom will withstand

So may be in some cases it is the weight which is important. I would guess that a modern high tech outboard is much more powerful for the same weight than one made 30 years ago.

As for the thrust.....
 
Flippin eck :eek: .Hope that never goes back in the water , no skeg on the outboard if my eyes are not playing up and i bet that windscreen is just waiting to shatter in someones face !!! .Shame ,obviously some effort went in to this boat .
 
michaelchapman said:
I would have thought there are two parts to the equation.

1) How much weight you can hang off the back

2) How much thrust the transom will withstand

So may be in some cases it is the weight which is important. I would guess that a modern high tech outboard is much more powerful for the same weight than one made 30 years ago.

As for the thrust.....
Click to expand...

On the flip side, a boat built late 80's, early 90's would be rated for the weight of a 2 stroke. Say a 1990 70HP. A new 4 stroke 70HP is bound to weigh more is it not?
 
That's mental. Shortly after the dinosaurs died out we had a Fletcher 129 with a Mariner 60 on the back, and that was utterly insane - 55mph on the speedo on flat water. With 100hp on the back, you can only hope that the engine is so old it could no longer make its rated horsepower...
 
It is not a simple question to answer for many reasons, it mainly comes down to how the boat was originally designed and classified, it could be designed for both for power by diesel or petrol engines, or both. Petrols produce more power and diesels less power but much more torque, so both these factors need considering.

Hull design is much more crucial, particularly today with computer design and testing software as this load is displaced right through the hull instead of being concentrated solely at the rear of the boat. Most modern boats cannot therefore have much more additional strain from overpowering put through the hull as it is marginally designed to cope with the load, and use the minimum amount of construction material.

Overpowering a boat could have serious implications, most notably is the issue of insurance, if it iis powered above the recommended maximum the insurance would almost certainly become null and void in the event of an incident and subsequent claim. Other problems may be the accelerated wear and fatigue which would damage many boats, particularly GRP or other plastic boats; this could lead to serious hull or superstructure cracking, particularly at high speeds or hull loadings in choppy water.
 
I always understood with small trailable boats the outboard size and hence weight limit was to protect the boat whilst being towed, too much weight rocking up and down whilst bumping down the road will produce far higher and different loads than it will ever see the water.
 
Wiggo said:
With 100hp on the back, you can only hope that the engine is so old it could no longer make its rated horsepower...
Click to expand...
According to the ad:

"got engine off a friend engine was running a year ago but has a very laszy starter motr engine will tern by hand"

So currently making 0hp. Whenever I see something advertised that doesn't work, but is claimed to just need a new battery or a £25 part to fix, I assume in reality its completely knackered, which is why they are selling it rather than just fixing it themselves.
 
i've had a 17ft fletcher running a 235hp o/b (old eng.maybe around 180hp-200hp)boat rated for 150hp.
now run a winner wildcat 17ft boat 5.7l v8(300hp+)boat rated for 170hp.. no problem's getting insurance and yes i have made claim's on both boat's before..
depend's on the boat how well it was made.weight,hull and build quality.i would imagine some boat's will take the extra power and some will just go to the bottom.
the main problem with the fletcher was the weight of the o/b.mostly when trailing the boat(bounce on the transom).and when the boat was in the water you could'nt stand too far back in the boat as the transom was only 1"" above the water when stationary..
bloody good fun though!!!!
 
You would have to be a complete pleb / idiot to run a boat with an engine whose Hp and weight exceeds the manufacturers maximums.
That maximum is there for a reason.

Even if you don't kill yourself and wreck the boat you may kill someone else and when the insurance claim (assuming you have bothered getting insurance which may be unlikely if you are that stupid in the first pace) gets that serious the insurance company will look a little more closely than for little claims and THEY WILL REFUSE THE CLAIM.
You may have pulled the wool over their eyes for smaller claims and they will not refuse to take your cash, but when it gets serious they will come and take a proper look.

You'll be mad to do it.
 
The weight of an engine is a factor, but not a great one while towing, modern engines have already gotten more powerful while reducing weight. If the engine exceeds the maximum weight of the boats original design it could be a problem, but not for towing as the trailer suspension absorbs most of the load, not the hull itself.

It is the way the power is dispersed through the hull which is the issue, thats why engines of boats are stipulated at a maximum size, and on a fairly calm water the hull loadings are significantly higher than when towing a boat on a trailer.
 
moonraker 36 said:
angling is the thrill of a throdding rod in your hand i'll say no more
Click to expand...
Mmm... I love speedboats, and if you look at the video in this thread you'll see someone who might consider even a 350ci block on a 170hp rated boat as not much more than angling.
That said, Nautibusiness' recommendation makes a lot of sense imho.
Of course if you know what you're doing - and you're aware of the risks involved - you can do whatever you want.
Frinstance, the driver in that video probably knows that if anything go wrong, he'll be dead at best and in a wheelchair at worst.
Not sure about his passenger, though...
 
with out getting personal.(like some)
which is more dangerous the overpowered boat being driven at say 30knts...just crusing along.
or the the 3m rib that is within it's max rating blasting through the middle of a load of swimmer's...
just because a boat will do 60+knts dont mean you have to go every were at 60knt's!

and i'm insured aswell 2millon liabilty

you get idiot in every walk of life having an overpowered boat, dont automaticaly make you one.
 
landlockedpirate said:
Theres been lots of discussion on here about putting more outboard power on boats than they were originally designed for. In general the feeling is that its ok, as long as the helm is experienced and the installation is done well. Back in the 80's my dad always slightly overpowered the family Fletcher ski boats so that they could be used for barefooting and some fairly fast mono sking.

But when does it become dangerous? Boats appear on Ebay from time to time that look stupidly over the top. These boats are usually old, with possible transom degradation or damage and the cheap prices mean they could be bought by newbies with no experience.

Heres an example, very little info, but I think its a Fletcher 129 that had a max engine size of 40hp when new. I would have happily put a 50hp on it but 100hp !



http://cgi.ebay.co.uk/fletcher-100h...tem&pt=LH_DefaultDomain_3&hash=item335f6b843c

Death trap, or just a bit of fun ?
Click to expand...

see the trouble with this boat mr pirate is that it prob.. has never been in the water with that engine fitted. i would say it prob will sink looking at the height of the transom..(i never said all over the top engines were a good idea)
 
Lots of different views, but IMHO the Ebay boat is well over the top, Fletchers dont have a huge amount of freeboard and the weight of the engine might sink it even before it starts.

If it ever did start, I think it would be flipped quickly in the wrong hands. Most of this board are experienced and can make informed decisions, newbie buyers on Ebay might not be that lucky.
 
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