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Old 26 March 2004, 15:39   #1
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Max rated Hp on boats - why not !!!!!!

Just been doing a little research and what I've noticed is that most have engines that are below the maximum hp allowed on their hulls.

take me for example 74hp and the hull can take 115 hp. there are numerous other examples on this site also !!!!

Apart from cost is there any reason not to chose an engine to the max hp allowed by the rib manufacturer.


Paul



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Old 26 March 2004, 16:13   #2
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Cost is one reason, But It depends on what your going to do with the rib and fuel usage and maybe a smaller engine at lower cost to buy and run will that weighs a bit less performs as well

But what the hell do I know dont get my boat till next saturday

Avon 620 with a mercury 135 optimax on a hull rated to 150hp

mmmmmmm have I got the right engine??

Thanks Paul
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Old 26 March 2004, 17:32   #3
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Quote:
that most have engines that are below the maximum hp allowed on their hulls.

Yep, know that feeling!
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Old 26 March 2004, 17:42   #4
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Just because the hull is rated to a certain hp doesn't mean it can take the weight of most engines of that size.

Ive found numerous times with various boats that a smaller but lighter engine can perform much better than an engine right at the very top of the weight bracket, not in out and out top speed but in the way to boat handles and reacts to trim.
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Old 26 March 2004, 17:43   #5
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In my boating lifetime I tend to choose next size up ocer the recommended max hp ratings though depending on weigth ratios as in many cases the manufacturer are using the same engine block and housing for up to three hp, so basically weight are same wether the engine is i.e. 90 hp and 125 hp and boat manufacturer rates his boat 110 hp I would go for 125 hp engine.
This will give me better performance and lower fuel consumption at economical speed.
Bogi
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Old 26 March 2004, 21:05   #6
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Well, for swedish people i can say it`s not the cost, we drive a lot with our engines and in 2 years (most of the time) the gasoline is over the cost of the engine.
Is it the same in UK or are we driving a lot in SWE?
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Old 27 March 2004, 02:39   #7
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On my new boat it was weight,I wanted a fourstroke and the lightest weight for the highest hp was the yam 100,although the boat is rated too 115hp,I wasnt told at the time,but now I have the boat manual,it turns out that the max o/b weight is 170kg so the yam at 167kg is just within,wheras the mariner/merc 90 at 175kg would have been just over!I,ve yet to see how it will perform although I have heard of a 5.5 assault with a merc 90 4 stroke that apparently went very well.
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Old 27 March 2004, 13:50   #8
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Hmmmm,

I was looking at the gemini 5.5 and ribcraft 5.85. the 5.5 can take upto 140 and the ribcraft 150. So a suzuki 140 would sit nicely on the back. But, most I've seen have a 100 or 115 on the tail. Now as the suzuki 140 is actually a little lighter why not opt for the 140 and use lower revs at cruising speed and have plenty left in the tank should one need the extra ooomph !!!!

Unless 140 is too much for these boats, if so why do the manufacturers quote those HP

whats the negative you lot out there who know alot more than I do - which, in my case, is sweet F A.

Paul
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Old 27 March 2004, 13:57   #9
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They will quote 140hp meaning it will hold some of the lighter 140hp engines. Fourstrokes and opti's are always going to be heavier than a bog standard 2 stroke.
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Old 27 March 2004, 14:05   #10
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Nah,

Weight isn't an issue - have asked them. As I said the 115 and 90 is heavier anyway.
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Old 27 March 2004, 14:08   #11
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Daniel,

whats your 6 mtr Osprey rated at as a matter of interest

Paul
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Old 27 March 2004, 14:34   #12
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I think max power is better, I find it difficult to believe that manufacturers of Gemini and Ribcraft's stature would rate a transome at a given horsepower without at least checking the transom would hold the weight of the three leading brands of engine.

Out of interest why should an Opti be that much heavier than a conventional two stroke, surely the fuel compreesor and electronics don't weigh that much more.

I don't see a negative myself


Isn't Top Melon a great example of Maxing out a boat.

Yummy
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Old 27 March 2004, 14:41   #13
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Country: UK - England
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Bugger, hope Ive done the right thing!

Anyone know the max weight of the engine for a Humber Ocean Pro 6.3?

The max HP is 200.

Nick
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Old 28 March 2004, 04:49   #14
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Hi Nick

Think its just a bit heavier than my 240HP Yanmar

Regards Gary
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Old 28 March 2004, 06:52   #15
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Isnt it a bit like cars?

We dont all drive around in Bmw M3 EvoII we choose engines that suit our purposes (even if we would prefer more).

I assume car manufacters sell more 1.8 petrol/diesel versions than v8 twin turbo nitorus supercharged versions.
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Old 29 March 2004, 05:56   #16
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Rating a hull for max HP, hasn't this something to do with the CE making of the boat.

I do belive that there is a rule in the CE making that states how to calculate the max HP for your boat.

something like:
(length * width * 15 - 33) / 1,15 = HP (allowed)

Don't hang me on this, it only from memory. The static values might be a bit off.

Rene
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Old 29 March 2004, 07:49   #17
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Our tornado is rated for max 225hp I think. However, yamaha do a 150 and 200hp with the same weight, whereas the 225 has the same as the 250 and 300! Ultimately we got the best power/weight with the 200. When going flat out, it certainly doesnt feel like a compromise

Ricky
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