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Old 30 June 2003, 13:47   #11
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Originally posted by jwalker
PS. go to Land&sea site and look for the outdrive extension which they make. It only fits the alpha one but it's interesting in principle anyway.

It's available for both Alpha and Bravo, and they offer a money back guarantee if it doesn't increase your top speed by 10%.

My only concern would be whether or not it was man enough to handle the extremes that you rib boys put your boats through!!
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Old 01 July 2003, 05:26   #12
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Doel-fins

Doelfins simply work by giving the boat a larger planing area aft of the transom of the boat. This in effect gives a greater trimming action due there location.
I would doubt very much if warranty would be an issue as the fins are widely accepted on the market place. If such large forces were being exerted on the leg the fins would break as they are made of plastic!
Trim tabs would do a similar job but can be very expensive and require a separate set of controls as well as screwing or bolting into the transom which isn't very desirable.
Doelfins and trim tabs simply allow a boat to perform closer to its optimum as they help the stern of the boat to run higher in the water and not dig in! This means the hull is more efficient therefore reducing fuel consumption etc..
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Old 01 July 2003, 08:03   #13
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Joe, when I trim out the leg of Magellan Alpha (which, unless the water is really flat, gives a very hard ride) the nose duly starts to rise and I have less wetted hull area.

However, before I get very far the prop starts to slip badly and I trim in until it again grips. Would Doel fins enable me to get the boat higher out of the water without slippage?
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Old 01 July 2003, 08:14   #14
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SNAP

I get the same Mike

In the trim range (upto the soft stop on the control which lifts the leg) I can only trim out about half way before I start to cavitate bad. I run mostly fully in or upto about 1/4 of the trim range out.

Spoke to Ribcraft and they said this was to be expected on a bigger diesel RIB as the trim had far less effect on the ride of the RIB than on smaller lighter outboard RIBS. However they still think I might need to play round with the props a bit.

Regards Gary
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Old 01 July 2003, 09:15   #15
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Can anyone point me to the "land and sea" site or any other which may discuss doelfins on diesel outboard legs?
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Old 01 July 2003, 09:50   #16
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Trim Cavitation

Sounds very similar to what was happening on the 11m! The boat always ran very well but on trying to trim the nose up that bit more on calmer days the props would start cavitating without having achieved any noticable difference in trim!
Now with the doel-fins fitted the boat also comes on the plane easier. What has been noticed about trimming with the fins fitted is that it takes much less trim on the leg to achieve more noticible bow trim!
I think you would find that you wouldn't have to trim the leg out as far to get the desired running angle on the boat so therefore you wouldn't be getting the cavitation.
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Old 01 July 2003, 09:53   #17
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So, you would recommend it's worth a go fitting fins on my heavy ol' 9m beast then, Joe?
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Old 01 July 2003, 10:21   #18
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Go Fit Them

They are so cheap to buy and take about 10 minutes to fit. If someone has a boat which they consider to run perfectly then it probably isn't worth fitting them.
However if there are obvious things like lack of trim or a boat running stern heavy then the answer has to be definitely fit them. You will more than likely end up with a boat which handles much better and is cheaper to run.

Just found one of there adverts in a magazine stating;

- Doel-fins improve overall performance even on well designed hulls.
- Save up to 30% on Fuel Consumption
- Faster onto the plane
- Greater stability
- Lower planing speeds
- Higher top end speeds

I say give them a go
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Old 01 July 2003, 10:26   #19
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Thanks, Joe. I'll give it a whirl. Anyone got any idea where to get the things in the UK?
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Old 02 July 2003, 16:00   #20
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Mike,

Try here: http://cgi.ebay.co.uk/ws/eBayISAPI.d...category=15263
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