Originally Posted by Stevenmb
Thank you for your replies, as a novice to boating ( been out couple times with my mates) I presumed that all 30hp engines are the 25hp engine just without them being restricted. The engine I have is a 2 stroke 2 cylinder ( 2 spark plugs ( sticker says one is16hp and other is 14hp) ). I also I understood that the transom can often hold more weight etc however they lower it as a way to cover their self from liability if a transom was to fail. My example of this is my boat is roughly 3-4 metres which states it holds a 40ph (2 stroke back then) however the newer boats which are the same size are rated to a max of 30hp( ie the hon waves ) however most of the avon sports only go up to 25hp. So being the same boat pretty my question is surely it wouldn't effect the boat at all as it's only 5 hp more then it states? I realise in terms insurance it might be an issue however I would have asked that once someone gave me there experienced knowledge about the issues it might cause. I'm sure plenty of people have put a bigger engine on a boat then stated. I obviously I wouldn't put a 50hp on a transom maxed at 25hp but surely a 30hp on a 25 wouldn't be that bad?
In a lot of cases it wont be a problem at all, but you need to have the experience to understand that. Older boats were much, much heavier than modern PVC sibs and so sticking a 40hp on an old Avon with an over engineered transom that weighed the same as the Forth Bridge wasnt a problem.
I will try to give you an example. The Zodiac Futura Mk2C Fastroller is rated to 25hp. With 1 person on board and a 25 the boat becomes a rocket ship, right on the edge of safe performance for a sib. It even starts to chine walk on the speed tubes if you get just the right amount of popple on the water. Stick a 30hp on it and it can go wrong very quickly, throwing the helm or even flipping the boat.
But at the other end of the spectrum, putting a same weight 25hp motor (instead of the stated 20hp max) on a fully loaded new Honwave T35 wouldnt be an issue (insurance accepted).
My dad over engined all of his speed boats in the 70's and 80's, mainly because we needed the performance for barefooting, but back then insurance was easy and 'Where there's blame there's a claim' firms didnt exist. These days its just not worth the risk.
Of course you could just ignore the advice and do it anyway .......