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Originally Posted by Pav
I've been puzzled by outboard ratings for a while. Transoms are rated for a HP. I assume this is actually related to weight rather than the actual HP? Am I correct on this?
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As Polwart says, strictly speaking it's both. I'll keep it simple - HP will try to twist the transom off the back of the boat, (the force from the propeller creates a moment as well as pushing you forward. the hull has to hoild that moment), and the weight will be related to the dynamics of the momentum of the engine as you bounce over waves / along the road / bounce it up a beach on it's trailer. (i.e how likely the transom is to stay attatched)
Quote:
Originally Posted by Pav
Also some outboards I see are rated 9hp but have been tuned to 15hp etc which confuses me even more! and I learn that some 15hp are infact 20hp outboards that have been limited?!
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Simply down to the economies of scale of mass production. You'll find if you take any manufacturer's range that two or three engines will haver the same CC, be the same weight etc. Strictly speaking the lesser power ones in a group will be restricted. (i.e your 9 tuned to 15 is actuially a 15 de-tuned to 9) Otherwise the cost of all engines would be well higher than it is now as more different parts would be required.
Quote:
Originally Posted by Pav
Understanding the above may be able to help me pick a small outboard for a paddleski. Its transom is rated 3HP.
<huge snip>
So going by the advised 3hp rating are there any outboards that come in light for the HP or any that offer a bit more grunt than others? <snip>
Obviously I am looking at 2nd hand 2 stroke outboards to keep weight to a minimum. Any suggestions on the better ones to look for re. light weight and grunt! in the 3 - 4hp bracket?
Thankyou.
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By going 2- stroke you're halfway there. If you don't mind your insurers laughing should you claim, (excedding that plate will gicve them their get -out clause), Evenrude did a ridiculously lightweight 4 Hp Twin that got slightly heavier after 1981 when they fitted a neutral clutch. It shared it;s leg / ggearbox with the 2Hp and so was about as light as it was going to get. Memory says it was in the 15-ish KG bracket.
If you can find old Brochures, what you want to do is find a 3Hp that is the same CC as the 2, etc. then ytou know you have the one at the top of the group. Ass Gibbo says, you can't go far wrong with one of those 3.5 Tohatsoos (I think they did a 3 as well)