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Old 05 May 2008, 17:58   #11
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Originally Posted by chorscroft View Post
...Having talked to a few people including the guy that designed the boat they think it would only do speeds in the low 30 knots e.g. 32, 33.
Why is it that they don't actually know the boat's speed?

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I know someone who repropped an 11m redbay and gained over 6 knots - is this unrealistic?
Very. At the speeds and weights you suggest for your boat an increase of 6knots is approximately equivalent to an increase of 100hp.
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Old 05 May 2008, 17:59   #12
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Conor,

It sounds like you have already spoken to the guys at Redbay about this, and didn't like what you were hearing. Whilst no one is infallable, and certainly there might be ways of pushing the boat a little bit faster by sacrificing something else - if the designer/builder/salesman isn't convinced then that says something. If anyone has a feeling for what that boat is capable of it must surely be them (or the current owner - who can't really be trusted as he is trying to sell it).

The detail in your post suggests the designer even gave some serious thought to the speed rather than the first number which tripped off the tongue.

But you might be better asking how often Redbay owners in your intended cruising area actually spend time doing > 30 knots anyway. Even on flat calm days its probably not ecconomical, esp with rising diesel costs.
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Old 05 May 2008, 18:11   #13
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Think of driving a car in say 3rd gear - pretty good acceleration but top speed not so good. Now think of 5th gear - great for top speed but useless if you need to accelerate out of the way of a falling tree!!!

In rough seas you won't be going very fast but you need instant response and the higher the pitch of prop the worse it gets. To be honest I reckon Redbay will already have got the best compromise they can out of those engines.

Trim tabs generate lift at the stern - this will make the hull run flatter and lift the arse end - this MAY overcome the extra drag they create but no guarantees. Still triim tabs are a good thing to fit anyway - if your bow is light it is good to keep the nose down into a head sea.

http://www.motortechmarine.co.uk/pro..._tuning_plans/

453 inc vat - expensive but cheaper than a dual ram Bennet or similar and easy to fit - to the right hull. You will have to check they will fit first - how much people will charge you is anyones guess!!!

I would buy the boat IF the price is right and look into chipping the engines - it should be possible but the marine market is much smaller than the car market so finding one may not be easy.
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Old 05 May 2008, 18:17   #14
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Codders, you are recommending these tabs again, have you actually fitted yours to your boat yet?
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Old 05 May 2008, 18:38   #15
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Quote:
Originally Posted by chorscroft View Post
The boat is 8.5 metres long and I would guess weighs under 2.5 tonnes including engines (is this a reasonable estimate?)
You may be surprised how heavy that RIB is... with the inboards, the wrap-around console and covered foredeck it may tip the scales at well over 2.5 tonnes, but impossible to guess as it all depends on the lay-up (ie the thickness of the GRP).

Here's a hand grenade: http://www.rib.net/forum/showthread....ighlight=steyr
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Old 05 May 2008, 19:40   #16
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but impossible to guess
not really - the redbay site lists the hull weight (ex engines) as 1171 kg. I assume that is ex. the canopy etc too - as it seems to be a general wt for all the 8.4m hulls. The engines are roughly 500 kg in total. redbay list the max loading as 1077 kg, so I guess about 2.75 tonnes all in, fully laden.
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Old 06 May 2008, 02:58   #17
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The original owner of the boat just commisioned redbay to do the hull and he the. Fitted the engines himself. Those boats were uwully fitted with the slightly heavier 165hp yamahas. This is why the boat may not have been tweaked correctly.
Codprawn - where would I go to find out more about the chips; the engines are around 1998 would they still have this feature?

Regards

Conor
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Old 06 May 2008, 03:18   #18
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Jwalker
They don't know the boats speed because the broker mainly deals in yachts - will find out actual speed on monday.

Polwart
The exact same hull design has been fitted with twin 240hp and did over 50 knots - the hull is capable it's just about drawing every last inch of power out of it.
As a current redbay owner myself I know that we would often cruise at around 32 knots. Although the boat is almost surely capable of this it wouldn't be doing it at economical revs.

codprawn
Is there a compromise to be made like say 4th gear XD how rapidly does the loss in acceleration/gain in speed come with each inch in prop size changed?
I have quite alot of experience in ribs - will I be able to tell driving it if the bow sits too high and if trim tabs would help?
Do those tabs have the same effect as other ones? All the 11m boats have bennet ones is there any real advantage?

Richard B
Don't worry have read that thread and it hasn't significantly altered my view on steyrs - I will see how they go on the testdrive.

Thanks in Advance

Conor
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Old 06 May 2008, 03:25   #19
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A set of tabs will help you get the bow down and at times will give you better speed as the boat is "running" at a better angle.
32-34 knots would be right for this boat with the engines fitted, my old 9.1 had twin 165hp Yamahas and did 35-36 knots flat out in perfect conditions, but more importantly could maintain a better rougher weather speed than anything else, so it is a bit of a trade of. I had around 70kg of chain in her anchor locker to help her head get down .
I have had 41.? knots from the 11m with very little fuel on board and flat weather and can get around 38 knots when full of fuel.
Andy
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Old 06 May 2008, 05:13   #20
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conor,

am I missing the point? you feel that this boat with these engines might be too much of a compromise to get the top speed you want. whilst redbays don't exactly grow on trees they are hardly hens teeth either. is this boat particularly cheap or something? otherwise if it doesn't tick your boxes walk away and wait for one that does.

I wouldn't be spending 40k+ on a boat, with the hope that I could rechip the engines to get it go faster unless I absolutely knew it could be done (i.e. steyr told me so). likewise if a 500 quid set of tabs would get an extra 20% top speed then why wouldn't the previous owner have put them on.

Not saying these things can't work - but if it doesn't perform how you want on the test sail then walk away unless you "can't afford not to".
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