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Old 13 June 2015, 04:17   #1
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Country: UK - England
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Make: Zodiac Cadet 285 FR
Length: under 3m
Engine: Mercury 6HP
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Zodiac FR 285 planing help?

Hi

I have a zodiac cadet FR 285, Mercury 6hp four stroke.

It will just plane, one up, after carefully checking tube pressures and experimenting with engine trim.

With heavier loads it reaches the point where the bow rises and it feels as if it is "trying" to plane but doesn't quite make it.

I appreciate planing is a tall order with 6hp, but I'm considering a couple of solutions.

Firstly, would a set of Zodiac Nautic - Accessories - Black flap kit (trim tabs) help?

Secondly, would changing the standard 8 inch pitch prop for a 7 inch give the necessary extra thrust to get on the plane?

Any other suggestions, apart from the obvious bigger engine? (Zodiac recommend 3-6 HP, maximum 8 HP)

Thanks

Pete
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Old 13 June 2015, 04:27   #2
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Country: UK - England
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Boat name: Bombard, Y-162
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Same old answer - more power or less weight. Anything else, ie adding 'go-faster' bolt on bits is tinkering round the edges.

Sell the 6 and get a 2 stroke 8hp or even 9.8.
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Old 13 June 2015, 07:59   #3
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Hi Pete

You should be able to plane with a 6hp,what sort of weight are you and yes you would be better off with less pitch.
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Old 13 June 2015, 09:32   #4
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If your boat is just on the edge of planing, then the tabs or a lower pitch prop MIGHT get you there, but then they might not. Its an expensive experiment that at best will simply mask the real problem.

For some reason Zodiac have always been conservative with max HP on the smaller sibs, 6hp is just not enough to plane reliably with more than a single light weight helm.

What Max said is spot on, swap the engine for a light weight 2 stroke, Yamaha 8hp or Tohatsu 9.8 are pick of the bunch IMHO in this size range.
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Old 13 June 2015, 15:32   #5
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Country: UK - England
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Make: Zodiac Cadet 285 FR
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Thanks, all.

I'm 85 kg, but as I said, the boat will plane with just me, and once on the plane it is possible to throttle back considerably without coming off the plane, so indeed 6hp would appear to be plenty, the problem being that at the point of getting on the plane the engine is only around half of max rpm, so is deploying much less than 6hp, hence my query about a lower pitch prop.

Your comments have prompted a few other questions:

New 2 stroke engines are not available. How old are the newest second hand ones? Are there any sneaky ways of acquiring a new one? Will a 2 stroke 8 match the 27 kg weight of my 6?

Zodiac's web site looks pretty but is in many ways useless. The page linked above tells you that trim tabs are available but gives no description of what they are for. Do they actually make the boat plane at lower speeds or with heavier loads? Do the flaps rub on the tubes and wear holes in them?

Can you really go above Zodiac's stated max power? Will the transom break, or the boat flip over, and will the boat be insurable?

Thanks again

Pete
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Old 14 June 2015, 04:08   #6
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>>> the boat will plane with just me, and once on the plane it is possible to throttle back considerably without coming off the plane, so indeed 6hp would appear to be plenty

Well I sort of understand what you mean but getting over the "hump" onto the plane is always the issue so any outboard that won't do that easily isn't big enough for rewarding planing performance.

It's not just about going fast either... if you ever get caught out in weather or a sea state that's challenging it's very useful to have an outfit that will hop on and off the plane with ease.

Having said all that many of us minimise the outboard HP on our SIBs to keep the carrying weight down off the water so getting over the planing hump is a frequent topic.

I would say something like a Yamaha 8hp 2-stroke would be the best compromise. You would be keeping within the Zodiac guidelines and in fact the power developed by that 8hp at the revs you are doing while at hump speed will be little less than a 9.8hp at the same revs. I'm pretty sure the Yamaha 8hp 2-stroke weighs 26/27kg.

The oldest "legal" 2-strokes were 2006 and many of that age are sold in almost as-new condition as many leisure outboards do very few hours over a year.

Yes there are devious ways to fiddle a new 2-stroke but having owned several recently aged from 2001-2006 I'd see little advantage in a new one.

I don't like trim tabs but it's just a personal thing.... I prefer to have the outboard power right in the first place.

Re overpowering the transom... well I've had a new Zodiac transom fail under heavy use with the correct outboard so I'm a bit wary. Leisure Zodiac transoms are a bit on the thin side compared to Honwave for example. The difference between a 6/8/9.8 will not greatly increase you chances of flipping.... more likely on a small SIB that's rated to and fitted with a 25hp.... and then only if handled badly. Insurance... you need to ask your company as they are the only people who's opinion matters.
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