Motor Size

[Mtx]

Hi All,

My brother in law has just bought a little tinnie for crabbing without having to take the big one out.

Apparenltly the boat is rated to have a 10hp on it.

what are the issues / legal problems etc associated with putting a 15 on as effectively they are the same motors in some cases.

Thanks

Jason

[caloundra]

good luck if you have an accident and try to make a claim on it

[NQCairns]

It's been done for years, insurance would have to prove that the oversized/weight motor was the contributing factor in the accident, or wouldn't insure in the first place.
It's actually up to you and how much common sense you apply to a situation, very few accidnts can be atributed to engine size but to operator error one of the most common is running up and over another boat from behind, always scary when someone tucks in behind. I do a quick hard left or right then run just behind but parallel hopeing they get the hint. sorry of track a bit.
There are no regulations regarding powering your boat just recommendations in Australia be them right , wrong, out of date etc etc.nq

[freefish]

Saw this done years ago. Replaced 25 with 40hp. All fine & went like a rocket until stress cracks appeared in the corners from flexing of transom. Local welder made a small fortune welding & bracing transoms.

[drdonjuan9]

yeah i think the strength of the transom really determines the power of the maximum size engine you can use. note if you use a 4-stroke then its much heavier also...... :o

[basserman]

i would say you shopuld be fine with the weight on the transom as their is not a grerat deal diffrence between a 10 and 15 but i would personly be going and putting some thing like the tohatsu 9.8hp on it as it is rated the same a a 10hp but weighs the same as a 8hp (like most modles the out side stays the same eg like the outside stays the same from a 6hp to a 8hp and a 10 is the same as a 15) so although it is rated for 10hp you would rally be getting the preformance of just under a 15hp thanks to the weight saveing (larger power to weight ratio) ;D

[Mtx]

He is looking at a merc 15 which I believe is the same weight as a merc 9.9

[basserman]

yeh but the thing you need to look at is how much heaver is the 15 than say another brands 10 or 9.8ect. with these thing is isn't always about the hp but more the power to weight ratio also the shape and size of the hull will play a big part

too small a size with too big a horse power could mean too much bounce in the frount and a very real chance of flipping over same with a flat bottom boat that was never desinged to go at speeds
i used to have a light car topper 11 foot flat bottom punt that was rated to 6hp and i put a 8hp on it (putting out the preformance of a 10hp thanks to the power to weight ratio) but it made the dam thing a bit to flighty and in the chop because it was on too much a plane it ended up cracking ever suport rib in the boat ;)

so i would recomend in looking at all the points before jumping from a rated 10hp and putting a 15 on it
and think of if the boat is really able to handle the new preformnce
as i said before a 9.8 or simular that has been made light shoud give you just as good preformance