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Old 20 April 2015, 00:53   #1
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Planing Angle and Trim

How to find the level of the planing surfaces on the hull and how to then set the outboard level (or at 90 degrees to level) ?


Planing angle ideal is ? 3-4 degrees up?
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Old 20 April 2015, 04:27   #2
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I use a highly scientific system called "The trial & error method", never fails & gets perfect results. There is no answer to your question & you'll run around in circles trying to find one. Trim varies constantly with sea conditions, load, speed etc. If you have PTT, the "standard" way is to trim down for setting off, get onto the plane & gradually trim up, when the prop starts to let go (cavitate) trim down a little until it bites. Different hulls react in different ways to differing amounts of trim. Some hulls will "Porpoise" with too much trim. You may find that your hull leans to much in a tight turn, this can cause "Hooking" or the prop to cavitate. There is no answer to your question. If you don't have PTT, then you need to experiment with the trim position to find what best suits your setup in most conditions.
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Old 20 April 2015, 05:35   #3
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Quote:
Originally Posted by Pikey Dave View Post
I use a highly scientific system called "The trial & error method", never fails & gets perfect results. There is no answer to your question & you'll run around in circles trying to find one. Trim varies constantly with sea conditions, load, speed etc. If you have PTT, the "standard" way is to trim down for setting off, get onto the plane & gradually trim up, when the prop starts to let go (cavitate) trim down a little until it bites. Different hulls react in different ways to differing amounts of trim. Some hulls will "Porpoise" with too much trim. You may find that your hull leans to much in a tight turn, this can cause "Hooking" or the prop to cavitate. There is no answer to your question. If you don't have PTT, then you need to experiment with the trim position to find what best suits your setup in most conditions.
This - vary the trim until the boat runs best.
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Old 20 April 2015, 05:40   #4
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Originally Posted by Christiananthony View Post
How to find the level of the planing surfaces on the hull and how to then set the outboard level (or at 90 degrees to level) ?


Planing angle ideal is ? 3-4 degrees up?
Generally the optimum angle of trim OF THE HULL BOTTOM / RUNNING SURFACE is indeed about 3-4 degrees, bow up.

However, this is rarely parallel with the tubes and also bears no resemblance to trim at rest.

Ideally what you are looking for is a hull that naturally wants to run at that trim with the angle of thrust as close to horizontal as possible.

Naval Architects spend an absolute age trying to optimise their design to achieve this.

For us "users" - all we can do is experiment with the power trim or trim pins to get the best result we can.
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Old 20 April 2015, 09:43   #5
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Very crude but.....at around twenty knots your stern wave will cross between 1.5 and twice the length of the boat behind you. Really, if you've got a trim gauge, trim the boat by "feel" in calm water at your normal cruising speed. The boat will generally feel a bit lighter and more responsive to the steering at the right point (and won't be porpoising).
Then note what your trim gauge reads and use this as a future starting point to adjust for the speed your going at, hole shot, weather etc. Generally your flat out max speed will be attained with the engine trimmed too far out for proper stability but every boat is different and every day is different......enjoy experimenting.....
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Old 20 April 2015, 11:46   #6
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Quote:
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I use a highly scientific system called "The trial & error method", never fails & gets perfect results.
...Eventually.



Quote:
There is no answer to your question & you'll run around in circles trying to find one.
Agreed. Part of the problem, I think is the definition of "correct trim". Pretty subjective description. As an example, I have a friend who runs a roughly similar size RIB to mine; she prefers nose-down in moderate swell (or pretty much anytime else), while I prefer a slightly-more-nose-up-than neutral attitude. Who's right? Probably both of us.

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Old 20 April 2015, 13:01   #7
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Very crude with me depends whose on board and I just move em round or leave them at the jetty
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Old 20 April 2015, 13:16   #8
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Boat'll go faster if you leave them all at the jetty.......but check none of them have the sandwiches !!!!
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Old 20 April 2015, 13:19   #9
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That's my thoughts
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Old 21 April 2015, 19:10   #10
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Aye, if you have power trim, I keep nudging it up until it doesn't feel right or the prop lets go at the slightest provocation then notch it back down by about a flick on the switch.

my old manual trim boat I quickly found out approx. right, then spent a year or so perfecting the art of choosing between the second & third hole form the top for the pun depending on the sea state & what I was doing (stop -0start rescue vs cruise)

Moving weight around also helps - on my old SR4 I'd generally use the FWD tank first as it improved the handling as it emptied.....

As you can tell I'm with Pikey on this one. You'll know when you find it...
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