Ouboard Engine Setup

[Paul D]

Studying on the web and I have an idea what is causing my lack of performance.

 

Symptoms are :-

 

Initial acceleration is fine.

Get to around 10 knots and then boat fails to lift on plane

Applying more throttle has no affect.

 

Then found this info ........ So off to test different trim settings once I get the engine tilt mechanism fixed ( SAL ordered the wrong parts .... )

 

What effect does trim have on boat performance?

The trim angle of the outboard/stern drive has a distinct effect on the planing angle of the boat, which, in turn, significantly alters top speed and handling. The engine/drive should be trimmed in for best start-up acceleration and shortest time to plane. The engine/drive would then be trimmed out for peak performance. If trimmed "in" (under) too far, the bow drops and the boat runs too wet. In this condition, top speed drops, fuel economy decreases, the boat may oversteer in one direction or the other ("bow steering"), and steering torque will increase (to the right with a right-hand rotation propeller). Occasionally, extreme trim under can cause a boat to list to the left (with a right-hand propeller).

 

If trimmed "out" too far, the propeller may lose its hold on the water. Fast vee-bottom boats may start to "walk" from right to left to right, etc. ("chine walking"), steering torque will increase in the opposite direction to that when trimmed in, and getting on plane may be difficult or labored. Porpoising of the boat may also occur.

 

 

[Newboy]

Paul, not being funny, but shouldn't the dealer who sold you the package sort this out? After all if your Orkney should plane with a 30hp and it doesn't, something is wrong, either the engine is not producing enough oomph to push it on the plane or the boat is at fault.

[Paul D]

Second hand boat ( although it was barely used ) , so no dealer to take back to

 

 

[Sinbad]

Hi Paul

hasnt your 520 got the mounting bracket with the holes in it to manually adjust the trim - admittedly its a bit coarse - but it does the job. Then its fixed as you know. I managed to break the manual handle off my Yamaha a few years back - seems to be a potential weak area, which doesnt see much grease !

 

my strikeliner is a bit different hull shape to yours, but its v sensitive to too much weight aft (fueltank being the max you can place back here).

 

perhaps for a demo on trimming outboards, you should ask Charlie to whizz you arround Poole harbour on one of the Club Ribs. trim settings do make a big difference to out and out planing hulls, but these have less than 50% of the hull actually in the water at full chat. Your 520, is semi planing and pushes a big bow wave of water infront of it, so it needs to climb the hill first. I doubt if the trim is the solution - sounds like a lack of power or torque.

 

have you tried A YAM dealer. you can buy an awful lot of investigative servicing for part of the price of an upgrade.

 

Just to make you sick, was doing 18-20 kts last season, flat water, one up with 25HP - as a guide.

 

Paul

[Afishionado]

As I understand it the Orkney hull of this type is that of a semi-displacement configeration, not a full planing hull.

I do not believe that with a 30, particularly a 4 stroke which develops it's full torque lower down the rev' range than a 2 stroke the boat loaded with tackle and bodies will do much over 15kts anyway. To push the boat further an immense increase in power would be needed.

It may be made to run better, and I believe that this could be obtained with a finer pitch prop allowing the engine to rev' a little free-er, but more power would only dig a bigger hole in the water at the stern for the back end to drop into.

 

I simply do not believe that these boats (as used in general in a normal gentle sea) are capable of 20kts let alone 30kts.

 

 

Mad Mike

[Paul D]

Paul,

 

I have a Honda on mine. The tilt mechanism is broken on it at the moment , but as you say, I can adjust the trim by moving the bar on the mounting bracket.

 

Plan for the weekend ( or as soon as my outboard has been fixed ) is to change the trim and to remove the aerofoil wings I currently have fitted.

Then test with a 9.9 X 9 prop to see if what it is like and then switch props to the 9.9 X 11 one.

 

My friend from work is convinced it was incorrect trim setting and I tend to agree as the boat was displaying all the symptoms detailed in my earlier post ( ie. Torque steer etc. ).

 

I am going to check all possibilities with regard to setup of the engine first before deciding to get a new engine.

 

Watch this space !

 

[Paul D]

Mike,

 

Who said anything about 30 knots ?

 

The 520 is supposed to be capable of 22 knots.

 

Mine is doing 10-11 knots flat out and you can tell something is amiss as if the power is being lost as the hull starts to lift. ( Also the boat lists to the right under power and it is not because I am overweight ! ).

 

15 knots cruising speed would be an improvement at the moment ( In the past 17 knots was readily achievable ).

 

 

[alun j.]

Mike,

Orkney describe these boats as 'performance hulls'.

I have a little 4 40 with a 15 hp. 4 - stroke Yam.

On a calm sea, on my tod, it quickly whizzes up to 20 + mph. [sorry, gps gives mph]......... but speed drops quickly with load 2 up = 13 max.]

 

Alun.

 

[Maverick Martin]

Semi displacement hulls will fly although they do give a hard ride at speed.. When I first got my last boat (Hardy 17 or5.2 metres) it had a 25hp outboard on it. That boat would plane with two up and do around 16/18 knots depending on the day. When I upgraded to a 40hp it would do around 24/25 and when I upgraded again to a 50 hp it would do 28/30 depending on conditions. If you are only getting 10/11 knots with a 30hp there is something wrong with either your engine, prop or set up although I am doubtful it is engine trim, agreed it can make a difference but 30 hp should easily push your boat onto the plane whatever the trim especially as a semi displacement hull has plenty of buoyancy at the front. I would be interested in seeing the results of your tests re prop and engine trim.

 

Martin

[blueboatdriver]

My Orkney 520 with four stroke yamaha 30hp reaches 22 knots with myself and my small son with me. With two adults it's more like 18 -20 knots. It is a bit bumpy at speed though.

[Afishionado]

Martin, yes you may have got the performance on a Hardy as they have a flatter bottom going aft, but the Orkney has a degree of 'rocker' so the lift property is lower.

 

Paul I am sure you must have talked to Orkney direct. What do they say? They should be able to give you their recommendation for pitch and dia' on a 30 O/B.

 

Removing the doel fin may not help. In fact it may make matters worse. The added lift at the back and the lowering of cavitation are things that improve performance.

 

Mad Mike

[Sinbad]

or try selling it - should go faster on the back of someones Mondeo !!!

 

"caveat emptor" or words to that effect.

 

70mph ( Alun) - full of gear.

 

Paul

 

[Newboy]

Paul if I was you I would take everything non essential off the boat with just enough gas to run for an hour or so. Start with no trim, no fin, but a bag of sand. Try different trim angle with the bag of sand at different position on the boat, record each speed and position of setting. Now try it with the fin and do the same.

 

What you want is the prop being perpendicular to the water and enough hull in the water for a settle ride, to much weigh at the front, hull line increases and prop pushing along as well as into the sea. Too little weigh at the front and your boat points skyward and your boat will be bouncing with its arse on the water.

[Adam F]

I would tend to think that it is an internal engine problem. as others have said a 30hp on your boat should plane it easily and 10-12 knots seems way to low.

 

We had a 30hp on Tara, and even with 4 up on a small boat like that we could get 14/15 knots.

 

Also you say that when you first bought the boat it was doing 17 knots, and has now dropped - if you still have the same prop than that cant be the problem?

 

When they serviced the engine did you mention the performance? Did they do a compression test and look to investigate why the engine seems under powered?

 

Whilst trim settings, luggage loading etc will make a differance (it can do on BW) it wont take 10 knots off your top speed - I think the issue is rather more major.

[Newboy]

How much does the orkney weigh including engine?

 

On my Sheltie, it was 350kg, plus 50kg for the Johnson 30, 2 adults-150kg, enough food+beer for a day 20kg, fishing gear 30kg, cooler+radio+equipments 20kg. With the Johnson being an old engine, it probably has less than 25hp and that wouldn't push the sheltie onto the plane, max was 14mph. You want at least 1 hp per 40lb and optimally 1 hp per 25lb of boat.

[duncan]

Paul,

 

Have been watching this thread quietly 'cos I don't have an Orkney 520 but feel I have to chuck in a couple of points as you are clearly sufferring at 11knots and want to sort it out!

 

1. At 11knots a 5.2m boat, with a hull length of less than that clearly, is already planning. It's not capable of travelling through the water in displacement mode much beyond 7knots and, if it did, would be sunk by it's own wake at around 7.5knots. It follows that we are therefore looking at optimising the relationship between the hull and engine from 11knots up (rather than playing around to get it over the resistance hump in the first place)

2. A boat/hull that size is very sensitive to weight distribution in creating the relationship between hull and water first, then when thats right the relationship between engine/transom needs to result in a horizontal thrust from the prop shaft (which if in place will provide near neutral steering moment). This right position can, as just said, be felt through the steering and be seen by the top of the engine cowling being parallel with the water surface.

 

If you don't have power trim then I would set the boat/engine up so that the propshaft is parallel to the aft third of the keel and go from there.

 

However, despite all the above, I would suggest from all the above that your engine is simply not producing it's full power for some reason (and that may include wrong prop).

[Newboy]

If as Adam said you had it onto 17knots when you first got it, and you haven't added much weigh to the boat and presume you haven't piled on the kgs, it's still the same prop, same trim angle and same boat, the preformance should on paper be very similar.

 

Have your mech clean the carb on the Honda, I'm sure I've read it somewhere they are prone to being clogged making it sluggish.

[sean]

You can get an aerosol carb cleaner; car spare shops stock it. I

[Afishionado]

You can get an aerosol carb cleaner; car spare shops stock it. I

[Sam]

mike your mad

 

nice to have you back livening up the conversation.

 

sam

[Paul D]

A little history here might explain why I am not so sure the engine is the problem.

 

Bought boat and runs fine. 17 knots ( on GPS ).

After 1 year of use speed drops and starts only doing 9 knots max.

Fitted Dolfins that Martin lent me. - bad move boat is unstable.

Played around with trim setting of engine to get better power

Changed prop to 9.9 x 9 pitch as current prop was damaged on ledge- better but still not right.

Removed Dolfins as they were bad news.

Have engine serviced - mucho improved.

.

.

.

Decided to fit smaller hydrofoil - seems OK but speed reduced.

Amended trim settings.

Boat still not performing as it should.

.

.

Engine serviced

Tried 9.9 X 11 prop

.

.

So I now have a much different setup to that I started with initially.

Therefore, my plan of action is going to be as follows :-

 

Remove fins

Put engine at same trim angle as it came initially

Test with 9,9 x 9 prop to see if can get revs up and 17 knots ( ish ).

Try varying trim angles.

Replace prop with 9.9 X 11 prop

Retest with varying trim angles.

 

I am 99% convinced I will find that the 9.9 X 11 prop with no fins and trim angle of about three notches out will improve things.

 

First I need to get the engine tilt mechanism repaired and then will report back.

 

If all the above fails I will "consider my options" regarding engine choice.

 

 

 

 

[Paul D]

Update :

 

Tested engine set up WITHOUT hydrofoil attached and using the 9.9 x 9 inch propellor with engine trimmed to three notches out ( as advised by Duncan - prop is parallel to the boat ).

 

Success to start - 17 knots with occasional 19 knots ( on slack water ).

 

I am now going to try with a 9.9 X 11 inch prop to see if speed is increased or if the pitch is too high.

 

Interestingly, as luck would have it, I saw a brand new 520 ( called Dream On ) at Wick today and even more lucky it was fitted with a 30 HP Honda.

Quick check of the prop on that motor and they are running with 9 1/4 inches X 12 inches. ( This seems to imply that my 9.9 X 11 should do ).

Also, the owner of this boat claims to have done 25 knots with just himself onboard ( per GPS ).

 

Still, I am happy with 17-19 knots, since any faster gets rather bumpy ( as Alun J spotted ). Finally fuel consumption is back down to nice low levels.

 

 

 

 

[duncan]

Great news Paul. Glad you are zipping about - even better that fuel comsumption is improved!

 

Phaeton finally went back in on Saturday and a 'shakedown' weekend (scarily) didn't highlight any major problems. Monday morning saw the list shrink to zero and I can now consider the planned 'improvements' rather than continue the fixes!

[Newboy]

Paul you don't want to be on wot for any extended time anyhow. 4 strokes are not designed to be driven at wot unless you want engine damage.

[duncan]

nearly all marine engines will have been set up for wot = 1 hour rating and a seperate continuos rating will be advised in teh operation manual.

 

Some smaller 4 strokes are set up to run all day at wot, most are not.

 

few people will travel for more than 1 hour at a time in a small boat so they don't even need to consider the issue and consider instead fuel consumption!

 

As an example my 4 stroke's (diesel) figures are:

 

2800 rpm - Fast cruise (still on the straight lline for consumption)

3100 rpm - Continuous rating

3300 rpm - Max power - 1 hour rating

3650 rpm - Governed max revs - only used when in danger of missing last orders or racing jet skis.