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Old 04 September 2009, 11:21   #1
Pav
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Small Outboard HP needed .. Which??

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?

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?!

Understanding the above may be able to help me pick a small outboard for a paddleski. Its transom is rated 3HP. I realise its a small outboard, but want to pick something as lively as I can, as paddeskis can still shift a bit when they are powered (ok, VERY slow compared to the ribs most the forum members use!). Its enough HP for some bass fishing etc inshore, but with the right power I should be able to fish the estuary if I avoid the main tidal push which would be a real bonus for me. I am not towing, racing etc! , just fishing and trolling lures inshore.

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? I know some dinghy users use outboards as small as 4hp for moving around inside the estuary.

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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Old 04 September 2009, 13:06   #2
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I used to have a 5hp single cylinder Mariner, nice little engine and light. My Longliner did about 5kts with it on and that was 16ft long.
It ran more or less on fresh air too!
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Old 04 September 2009, 13:34   #3
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tohatsu 3.5 great little engines
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Old 04 September 2009, 13:41   #4
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Quote:
Originally Posted by Pav View Post
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?
no - then they would be rated on weight. It is just as easy to stick "50 kg" in the manual/plate as it is to write "15 HP". Indeed many write both. Technically its not the "transom" that's rated its the whole boat.
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Old 04 September 2009, 18:52   #5
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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?
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)

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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?!
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.

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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.
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)
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Old 04 September 2009, 19:03   #6
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tohatsu 3.5 great little engines
I'll second that, was a bit skeptical on the performance of this small, light weight portable engine untill was called by the J-24 Sailboat Asociation, needed 3.5 engines fast, Tohatsu Japan shipped 15 units relatively fast.

Starts at the second pull, had every one on between idle and start position in a water pool for 1 hour and 2 hours at sea pushing up to 1/2 throttle. Was amazed at the nice push performance of these little monsters. When break in 5 hours time has elapsed, will be pushing 1.5 ton J.24 sailboats. Highly 2 strokes recommended, 3.5 B-2 model if still available in your country.

Happy Sibbing
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Old 04 September 2009, 19:33   #7
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I'd be tempted to track down a mint one of these:

http://cgi.ebay.co.uk/Yamaha-Malta-3...d=p3286.c0.m14
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Old 05 September 2009, 05:50   #8
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Thankyou all for replies. It makes a lot more sense to me now! 9D280 really useful explanation.

The Tohatsu 3.5 looks ideal. Can you still find new stock for the 2 stroke? , or have these all dried up now?
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Old 06 September 2009, 12:22   #9
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Spoke to a guy today who has the same model paddleski who had been running it with a 3HP. His comments were that it would easily take a 4-5HP.

I am considering the Tohatsu 3.5HP as advised, but anything else up to 5HP worth considering for weight? I kinda understand now that i am looking for the outboards that are unrestricted so offering the most HP per weight.
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Old 07 September 2009, 12:10   #10
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Spoke to a guy today who has the same model paddleski who had been running it with a 3HP. His comments were that it would easily take a 4-5HP.

I am considering the Tohatsu 3.5HP as advised, but anything else up to 5HP worth considering for weight? I kinda understand now that i am looking for the outboards that are unrestricted so offering the most HP per weight.
Check Tohatsu 5 HP, 2 strokes if available, has incorporated gas tank, weights 19 KG compared to 13.0 Kg for the 3.5 HP.

5 & 4 HP are same engine weight, 102 CC block.

Happy Sibbing
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