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Old 23 April 2006, 05:21   #1
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To list or not to list?

Ok, now I'm confused ...

I am told by those illustrious people at Scorpion that my boat needs to have a list to counteract the engine/propellor torque (8.5 mtr boat, 250hp Etec).

Apart from the fact that I shall be keeping my boat in a marina and a list will not look or feel great, I am interested to know members of the Forum's views on whether or not you believe that having a list is a good thing and if it actually makes a positive difference.

I thought that engine offset was all that was needed to offset propellor or engine torque.

I am not an engineer (I guess that's obvious!) but it doesn't seem entirely logical to me that a boat should intentionally be built with a list. In my case, this will be caused by 2 x 120ah batteries on the same side.

I would welcome your thoughts.

Thank you!

Chris.
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Old 23 April 2006, 05:40   #2
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Quote:
Originally Posted by Chris Murray
I thought that engine offset was all that was needed to offset propellor or engine torque.
Engine offset will create a list. On my previous boat I used engine offset, consol offset and my weight to counter prop torque. Plainly the boat would have a list at rest but it ran straight. However, I feel trimtabs are a better way of dealing with the problem because listing will develop in beam sea situations and this can be countered irrespective of which side the wind is blowing from. I find there is also another plus. If the tabs are mounted along the hull V rather than horizontally, there is a slight steering moment generated with a tab down. So, when countering the list generated by the wind, the tab also causes the boat to steer slightly towards the wind and this prevents the driver having to constantly compensate for drift.
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Old 23 April 2006, 05:45   #3
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this is how i see it...

If you don't have some weight on one side to counteract the prop torque, the boat will list while at speed, which is worse than having a list at rest/slow speed. I don't think it would be that noticable on a rib that size anyway?

The other thing to do would be to have two engines like the scorp I saw in yarmouth yesterday...twin 275hp verados!
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Old 23 April 2006, 05:50   #4
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Or buy a boat that doesn't need a list to make it run straight?
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Originally Posted by Zippy
When a boat looks that good who needs tubes!!!
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Old 23 April 2006, 06:02   #5
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What boat would that be, Cooks?

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Old 23 April 2006, 06:08   #6
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Quote:
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Or buy a boat that doesn't need a list to make it run straight?
Cookee has got in there first, Andre will be along in a minute
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Old 23 April 2006, 06:15   #7
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Followed by Leeway. That'll be why there's a hook on one side...


Oops, did I say that?
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Old 23 April 2006, 06:21   #8
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Originally Posted by jwalker
Followed by Leeway. That'll be why there's a hook on one side...


Oops, did I say that?
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Old 23 April 2006, 06:34   #9
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I don't know anything about the science of this so I should probably keep quiet but....

Mine doesn't list at any stage from rest to full speed (well it didn't until the backside fell out of the tube on one side...) it doesn't have any trim tabs on the hull, and the engine is mounted in the middle. Admittedly it "only" has a 115 on the back, but it doesn't appear to have any negative effects from prop torque, you don't notice anything apart from if you take off from rest to full speed you need a very small steering input to keep it in a straight line.
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Old 23 April 2006, 06:50   #10
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Thanks JW,

This is the sort of info that is most helpful.

I do have trim tabs fitted - not much else at the mo but yup, the tabs are there - along with an awesome radar arch and "Tri-lens".

Further comments would be appreciated - Thanks!

Chris.
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Old 23 April 2006, 07:22   #11
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I assume they are suggesting this as using a trim tab all the time to counteract torque effect will cause extra drag?
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Old 23 April 2006, 07:26   #12
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Originally Posted by codprawn
I assume they are suggesting this as using a trim tab all the time to counteract torque effect will cause extra drag?
Absolutely minimal. It just needs to be skiffing on the water. When using my tabs for counteracting listing, I notice no change of speed.

I'd listen to Scorpion, they'll know their boats best.
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Old 23 April 2006, 15:55   #13
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Hi Chris
We had the Same probleam two batterys etc.
All i can say is have the trim tabs, If you are around in the next two weeks
You can come out with us and see for your self.
I bet Graham recormends them to you, and i know it seams that you just keep speanding but it is worth it.
Roy
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Old 23 April 2006, 17:12   #14
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If Scorpion say you need it then you do!. They know an awful lot more about building and rigging Scorpions than anybody else on this forum.

Call me old fashioned but I dont think think they are gonna fkk up their enviable reputation by rigging a boat wrong.
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Old 23 April 2006, 17:14   #15
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Quote:
Originally Posted by Rogue Wave
If Scorpion say you need it then you do!. They know an awful lot more about building and rigging Scorpions than anybody else on this forum.
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Old 23 April 2006, 17:17   #16
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apart from Jasper obviously!
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Old 24 April 2006, 03:43   #17
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One thing I will say about tabs. Remember to lift them when you moore up. Last season I forgot to do this on a number of occasions. One notable time was after using one tab, well down, in a beam sea. We stopped in a harbour for lunch and afterwards we left at its side entrance, turned along the harbour wall, opened the throttle and met the sea side on with the wrong side tab well down. That wakes you up. They don't half seem slow to move when you need them in a rush!

I've bought an auto tab retractor but it's not yet fitted so can't comment on performance.
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Old 24 April 2006, 09:10   #18
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Quick / slow?

What tabs are they fitting? They normally fit twin ram Bennett tabs. These are painfully slow.

Some manufacturers (cruisers mainly) are fitting Lenco tabs. These are quick acting and the standard switch panel has built in position indicators. Not sure how robust they are though.
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Old 24 April 2006, 15:51   #19
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Quote:
Originally Posted by Roy Smith
Hi Chris
We had the Same probleam two batterys etc.
All i can say is have the trim tabs, If you are around in the next two weeks
You can come out with us and see for your self.
I bet Graham recormends them to you, and i know it seams that you just keep speanding but it is worth it.
Roy
Thanks Roy for your kind offer!

The hull does actually have trim tabs attached (Bennett). I had these on my last boat (only single rams) and they made a significant difference, especially in cross winds or just to counter-balance excessive weight on one side. The new boat will have dual cylinders so may be slower to respond but should be considerably more robust.

On this basis, I should think that a limited list to starboard plus use of trim tabs, as required, should be a good compromise - and keep the tubes out of the water, while in the marina.

Regards,

Chris.
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Old 27 April 2006, 06:05   #20
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Quote:
Originally Posted by jwalker
Followed by Leeway. That'll be why there's a hook on one side...


Oops, did I say that?
have you ever seen a leeway? or know anyone with one? obviously not judging by a stupid coment like that...
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