Planing Angle and Trim

Christiananthony · 20 April 2015, 05:53

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?

Pikey Dave · 20 April 2015, 09:27

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.

Searider · 20 April 2015, 10:35

Quote:

Originally Posted by Pikey Dave

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.

Searider · 20 April 2015, 10:40

Quote:

Originally Posted by Christiananthony

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.

Last Tango · 20 April 2015, 14:43

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.....

jyasaki · 20 April 2015, 16:46

Quote:

Originally Posted by Pikey Dave

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.

jky

mick · 20 April 2015, 18:01

Very crude with me depends whose on board and I just move em round or leave them at the jetty

Last Tango · 20 April 2015, 18:16

Boat'll go faster if you leave them all at the jetty.......but check none of them have the sandwiches !!!!

mick · 20 April 2015, 18:19

That's my thoughts

9D280 · 22 April 2015, 00:10

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...

Roflhat · 23 April 2015, 20:03

They reckon 3 degree trim is the best, they being the guys on boatracingfacts. Ideally your trim would be when the centre line of the prop is parallel to the water surface, as this is when you're prop is delivering it's maximum forward thrust. Unless you have a highly optimized hull which developes exactly the right amount of lift at a certain speed you'll need to trim your engine to compensate for the lack of/too much hull lift.

With thundercats, I find that at speeds upto 50 knots its quite stable with about neutral trim. Anywhere over this and you start having to tuck the engine in as the amount of air flowing between the hulls generates too much lift. This is why the power required to achieve higher speeds is exponential, you're basically fighting the lift generated by the hull by using the engine trim to push the bow back down.

Without re-designing your hull to suit your setup specifically, the best you can do is trial and error

. If you're chasing numbers props are the way to go, get yourself a tacho and a GPS

Christiananthony · 24 April 2015, 02:53

Interesting. My inclinometer is too sensitive for anything but a flat calm. Very difficult to get an accurate reading which I guess would only be an average over time since hulls moves around alot.

Some sort of dampening I guess or an artificial horizon from an aircraft.

Another problem is where on the hull to is the horizontal planing surface? (to zero the inclinometer)

I put my 24kg battery in the forward anchor locker and this helps alot. Might consider 2 fuel tanks say of 40-50 liters of fuel each. One as far forward as possible and one after. Then a transfer pump.

Cant understand why the prop would run at anything other than horizontal but how to measure this? short perhaps of using a artificial horizon (gyro)

My setup is a 2008 FT60 Yamaha on a 2008 Gemini 550 Waverunner. Best fuel economy appears to be at 3-4 knots, 800 rpm = 180ml/km. This is using a 25 inch pitch prop and 600 kg total displacement. I also use motor speed controller (Pulse width modulator) on the high pressure fuel pump and turn the pressure down to 18psi lower than this and she starts to misfire. I am looking for an air /fuel mix ratio meter to install into #26 plug on the exhaust cover. Not sure which is the best one.

Why is the water temp soooo cold at 67 C. ?? (Checked the sensor,OK in spec.) Checked the thermostat fully open at 70.

The best fuel economy planing at 18 knots loaded to 600kg and 2900 rpm is 218ml/km. Bottom clean and hullkoted (Mclube). I think this could be better. Would love to get my hands on a Smart 3 cylinder diesel 65hp engine! They weigh in at about 65kg not including heat exchanger or stern drive.

Pikey Dave · 24 April 2015, 08:10

Hmm! I think you need to look at fitting a flux capacitor between plug 1 & 2. Adding a little jet1a to the fuel mix could help, about 2pico litres per litre of fuel should just about do it. It sounds as if your half housing bearing on the laffing shaft could do with balancing. As a last resort you could try enriching the Dilithium matrix in the GRP hull to reduce the friction co-efficient. Keep us updated how you get on, I'm off to the delta quadrant for a bowl of Gagh.

.....sh1t happens.......

paddlers · 24 April 2015, 08:53

Roflhat · 24 April 2015, 09:10

hahaa!

You should try moving as much weight towards the back of the boat as possible, that will help reduce the amount of hull in the water which will give better performance and economy. This is why trimming up often makes boats faster, although the prop is running at a less effective angle it's getting the hull out of the water. It's all a trade off, just go out and try various settings.

Christiananthony · 25 April 2015, 03:33

She runs faster with less load. Even one person less (40kg,wife) and will do 22 knots easily and this is with a 25 inch pitch prop and wot 2700 rpm. I try to reduce fuel pressure to compensate for the low vacuum (and richer fuel mix) in the intake manifold which is the only reason I think over propping gives you bad fuel economy.

Has anyone tried a small wing below the prop, something the size of the popular dolphin wing on the anti-cavitation plate?

cptsideways · 25 April 2015, 09:45

On our deep V hulled Four Winns adding wings to the outdrive dropped planing speed from 24mph down to 16mph the difference was massive. Obviously some extra drag at higher speed. But the additional lift it provides at lower speeds made it hugely more practical, also means you can see where you are going lol

Next job I'm moving the 44gal fuel tank forward a foot or so, my bet is it will be better again.

Pikey Dave · 25 April 2015, 10:17

Quote:

Originally Posted by Christiananthony

with a 25 inch pitch prop and wot 2700 rpm.

What ever you do, do it quick, that engine hasn't got long

Christiananthony · 25 April 2015, 10:35

Oh! My 2nd boat happens to be a 268 vista. Has the Volvo duoprop. The Volvo petrol engine was damaged because the shipper didn't drain it properly. So bought the VW 2 liter CR TDI mapped to 180hp. Great solid boats. Will be trying a wing on one the stern drive but I think below the propeller since I suspect the cavitation plate mounting is too high

Last Tango · 25 April 2015, 14:22

Have you actually looked at the Doelfins at WOT. You're trimmed out and there's no transom cavity refill that close to the boat at high speed (40+). They don't cause any drag because they're clear of the water altogether.