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Old 18 September 2011, 15:39   #1
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Maximum horsepower or maximum weight

Just wondering what is best to go by, either maximum horsepower or maximum engine weight,
IE, what are the problems with going over the maximum stated horsepower is you are well under the maximum weight, say 50 kgs.
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Old 18 September 2011, 16:01   #2
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Insurance...

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007
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Old 18 September 2011, 16:03   #3
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You don't really want to be pushing your transom through your boat do you or flipping it over backwards?
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Old 19 September 2011, 00:49   #4
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Over weight, break the transom
Over power, flip you out of the boat
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Old 19 September 2011, 10:42   #5
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Over weight, break the transom
Over power, flip you out of the boat
Weight - don't need to use the max HP (but then why have it ?)
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Old 19 September 2011, 11:45   #6
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Both.
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Old 19 September 2011, 12:19   #7
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don't need to use the max HP (but then why have it ?)
Tell that to your insurer or the agency certifying the boat as safe and seaworthy.

I don't understand how a boat can accept a motor vastly above the rated power while staying within weight limits anyway. That suggests to me that the transom is widely overbuilt (heavier and bulkier than necessary compared to the remainder of the hull design).
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Old 19 September 2011, 12:53   #8
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I don't understand how a boat can accept a motor vastly above the rated power while staying within weight limits anyway. That suggests to me that the transom is widely overbuilt (heavier and bulkier than necessary compared to the remainder of the hull design).
Simple the boat/transom is designed to take say 90 HP, so to take a modern 4 stroke that means it needs to be rated for something like 180 kg. Now you can get a 130HP etec, 125 HP optimax within that limit. If you shop around for an old 2 stroke you can probably get that power way under the weight limit. The rest of the boat might not be lightly build just flighty / likely to chine walk etc with too much power.
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Old 19 September 2011, 14:32   #9
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You have more RIB manufacturers over there ,but at least with Avons and Zodiacs which make up probably 80% of the US market they have not revised their transoms to accept heavier outboards. You'll often see a transom rated for 70hp but only be able to find a 50-60hp to fit it since there are very few (new) 4 stroke 70hps within the weight rating developed for a 2 stroke. (the reverse problem) Worse is trying to find something like a 40hp short shaft which many Zodiacs in the ~15ft size range take. They just aren't available anymore.

Once you get into the 90hp+ department there are very few RIBs over here being built/imported in that size range. So upsizing a 90hp four stroke to a 125 optimax really isn't something our Ribbers have to worry about or deal with (even if they wanted to).

Most of the Avon's and Zodiac's mentioned above are 8-14ft tender sizes.
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Old 20 September 2011, 04:49   #10
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Simply 'coz the Avons are maily sold as commercial / military where the emmissions rules don't apply so they can carry on using 2- strokes!

Puit it in prespective, when mine was built the average sub 100 Hp engine had 2 cyls. I have a 110Kg / 60Hp limit.... there's some 3 cyl autolube 2- strokes out there too heavy for mine!
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