lean to port and Chinewalking on a Humber Ocean Pro 6.3

[lifeboatman3]

Thanks. I need to go for a run to see the rpm as I can't remember looking. The prop is a stainless 3x15x19p.

Originally Posted by Limecc

A starboard offset might contribute but I recall a Willard RIB with this issue and it was caused by cupping on the prop which in turn affects the shape of the thrust cone and the amount of torque reaction. It was also suggested to adjust the skeg anode in another thread linked below:
Ribeye leaning to Port when under power

Need details of prop pitch and the rpm at 34kn to calculate if it's right. Seems slow to me. By all means you should optimise engine height (as high as poss) and personally I'd centralize the engine unless the space is needed for an aux. It was probably offset on purpose to counteract the torque roll but I'm not sure if it was moved in the right direction or not. Different prop is probably the cure.

[Limecc]

Originally Posted by lifeboatman3

Thanks. I need to go for a run to see the rpm as I can't remember looking. The prop is a stainless 3x15x19p.

Using:
BF175 V6 24v 3.5L
WoT 5000-6000rpm
Gearbox ratio 1.87
Estimated slip 10%
19" pitch

Results:
34kn = 4,500rpm
37.6kn = 5,000rpm
41.4kn = 5,500rpm
45kn = 6,000rpm

It's not pulling max rpm and it might actually if the engine height is optimal. Usually start with the AV plate level with the hull and raise one hole (3/4"). Mine doesn't ventilate at two holes up, wish I'd gone straight to that.

When the engine height is correct you can estimate the prop pitch needed, decide if you want a three or four blade, which model/brand and where to buy. Also Steel Developments could tweak your old prop (I think it's £75 + p&p), but because of the leaning, unless it's got cupping to be removed you're probably best advised to go with a different design.

[lifeboatman3]

Thanks. Just been for a run and the engine max rpm is 4000 trimmed all the way down and at max trim is 4800rpm. I can raise the engine one hole higher without drilling more holes. Once it's on the trailer I will check the hight of the cav plate to the keel on the boat. Do you think lifting will help the rpm too? I'm happy with the speed as it is but just want it right and not leaning to Port as much

Originally Posted by Limecc

Using:
BF175 V6 24v 3.5L
WoT 5000-6000rpm
Gearbox ratio 1.87
Estimated slip 10%
19" pitch

Results:
34kn = 4,500rpm
37.6kn = 5,000rpm
41.4kn = 5,500rpm
45kn = 6,000rpm

It's not pulling max rpm and it might actually if the engine height is optimal. Usually start with the AV plate level with the hull and raise one hole (3/4"). Mine doesn't ventilate at two holes up, wish I'd gone straight to that.

When the engine height is correct you can estimate the prop pitch needed, decide if you want a three or four blade, which model/brand and where to buy. Also Steel Developments could tweak your old prop (I think it's £75 + p&p), but because of the leaning, unless it's got cupping to be removed you're probably best advised to go with a different design.

[Limecc]

You have two problems:
1. Planing is on the Port chine
2. Top speed is too slow

Your tests confirm the theory, you're not getting into the WOT range, if it did it might pull through to max rpm. Whether or not there's a problem with the engine, at those revs you might only be developing 140-150hp.

Raising it can be worth a pitch or two of prop so get it as high as you can. You are advised to re-drill in any case, I believe any engine offset should have been to Port not Starboard. Your offset is probably making the lean worse not better, heavy items and helm position can be offset to Starboard but not the engine causing the issue.

I had to re-drill the lower holes of mine because I could only raise it up one, they hadn't used the standard drilling template. Used G-Flex 655 and chopped up glass fibres to fill the holes, dowelling is inadvised because the grain direction is wrong and it won't compress equally with the transom core.

Lazy way out is to simply fit a 17" prop. You won't lose any speed because it will rev higher, and a different prop *may* solve the torque roll. *In theory a prop design with a narrower thrust cone (high rake, no stern lift) will help. Best to take the trouble and set it up properly though.

[Matt]

I think this is incorrect. When a (normal rotation) motor is offset, it's to the right/starboard. However, consensus is generally to just mount in the middle and put the batteries, aux motor etc on the stbd side if needed.

But other than that, does sound like it needs some setup work as you suggest.

Originally Posted by Limecc

I believe any engine offset should have been to Port not Starboard.

[beerbelly]

Originally Posted by Matt

I think this is incorrect. When a (normal rotation) motor is offset, it's to the right/starboard. However, consensus is generally to just mount in the middle and put the batteries, aux motor etc on the stbd side if needed.

But other than that, does sound like it needs some setup work as you suggest.

mines offset to starboard

[69cmw]

Originally Posted by beerbelly

mines offset to starboard

Correct [emoji106]

[Limecc]

Originally Posted by Matt

I think this is incorrect. When a (normal rotation) motor is offset, it's to the right/starboard.

As I said I'm not absolutely sure so it's good if there's a consensus.

Here's my thinking. The centre line of the keel is the pivot point, having the weight of the motor to Starboard is good but has a lesser effect on the plane. The propellor pushes the starboard side of the boat up and out of the water. If the motor is mounted to Port and the other side of the pivot, it's so much harder to pull the starboard side up because the leverage and opposing weight to Starboard of the motor is greater.

It helps to imagine extremes. If you had one engine and no transom, only the option to mount it on one of the tubes, I'd mount it to the Port tube, then it's trying to lift the entire stern, instead of just it's own weight were it on the Starboard tube.

Alternate theory awaited..

[Limecc]

Originally Posted by Limecc

Alternate theory awaited..

I have one

You have a car wheel to change, a dodgy handbrake and tight wheelnuts at 9 o'clock and 3 o'clock. Before you jack it up you want to crack the nuts. You apply the same upward force on the wrench to try and loosen the nuts in turn. The 3 o'clock (Starboard) nut will roll the car more easily than the 9 o'clock (Port) nut.

[Matt]

…… . .

[jwalker]

The engine is correctly mounted when over to starboard. 4" is a lot but if it's listing to port it's not too much.

Your engine is overloaded at the wot revs you are getting. Set your engine height on the transom first and check the performance and wot revs. If they're still too low you need to change your prop pitch. Don't be tempted to do two things at once, eg. change pitch and number of blades.

Also, for general use don't lift the engine too high, you'll compromise the rough water handling. 25mm is a good general setting.

I note your profile shows a 6mtr plus boat and only a 115hp engine, I'd guess a 15" or 16" prop pitch for that setup.

Edit: Forgot to say; be sure of your wind direction when testing for listing because your boat will list into the wind. ie. If the boat is running correctly, when the wind is from the port side it will list to port, when it's from the starboard side it will list to starboard.

[lifeboatman3]

Thanks for the tips and advice. I have looked and the max I can raise is 1 hole. I could drill a new hole but it's going to be just to close to the top of the transom and not strong enough. So lifting will be the 1st job and then try. 2nd option will be fitting another prop to see if this helps.

[lifeboatman3]

Images of the engine trimmed right down and about half way

[Pikey Dave]

Originally Posted by lifeboatman3

Images of the engine trimmed right down and about half way

That’ll stand coming up another hole.

[Limecc]

Originally Posted by lifeboatman3

Thanks for the tips and advice. I have looked and the max I can raise is 1 hole. I could drill a new hole but it's going to be just to close to the top of the transom and not strong enough. So lifting will be the 1st job and then try. 2nd option will be fitting another prop to see if this helps.

Shame. This is how it is for mine. I had to re-drill the lower holes not the top. Top hole centres are 47mm from top of transom.

[beamishken]

Looking at those pictures it looks like the transom has a significant rake on it & when your fully trimmed down the engine is pushing the stern up significantly I'd expect some odd handling with the engine trimmed right down. Id look at moving the trim limit pin out a hole or two to prevent trimming in too far & try & lift the engine up a hole & try it again. I ran a ski boat years ago with a 90 yam which usually ran with a 19p prop & it ran great but occasionally would fit a 21 if we were just going for a run with only 2 folk aboard. It was definitely faster but if we then loaded it up or tried any tow sports with the 21 it had similar handling characteristics to those your experiencing.
My first step would be limit the trim in & lift the engine if possible, then try & beg or borrow another lower pitch prop to try

Sent from my SM-G950F using RIB Net mobile app

[beerbelly]

Originally Posted by beamishken

Looking at those pictures it looks like the transom has a significant rake on it & when your fully trimmed down the engine is pushing the stern up significantly I'd expect some odd handling with the engine trimmed right down. Id look at moving the trim limit pin out a hole or two to prevent trimming in too far & try & lift the engine up a hole & try it again. I ran a ski boat years ago with a 90 yam which usually ran with a 19p prop & it ran great but occasionally would fit a 21 if we were just going for a run with only 2 folk aboard. It was definitely faster but if we then loaded it up or tried any tow sports with the 21 it had similar handling characteristics to those your experiencing.
My first step would be limit the trim in & lift the engine if possible, then try & beg or borrow another lower pitch prop to try

Sent from my SM-G950F using RIB Net mobile app

my humber has a similar rake when trimmed all the way in but i dont experience any unusual handling at all even when the outboard trimmed right down .i agree and at first thought it looked odd but it runs fine .my outboard was initially supplied fitted with the av plate an inch and a half above the keel line but i experienced bad prop slip whenever i tried to trim out i dropped it to the last hole so the av plate was almost level with the keel and that fixed it .i then discovered i was seriously under propped and went up a few pitches to a 19p and that helped .i haven't yet lifted the outboard back up to see if i can run it where it was originally with this set up .

[Limecc]

Originally Posted by beerbelly

so the av plate was almost level with the keel and that fixed it

I recall you have a Mercury Spitfire prop:

Originally Posted by beerbelly

i have a 5.5 destroyer with a 115 mariner comand thrust and i find it very comfortable in most of the sea states i go out in i usually cruise at 25 knots but even if it kicks up rough i can keep to a steady 20 knots it will usually do 36 knots flat out i am using a 19p mercury spitfire 4 blade that allows 6k rpm easily but gives very good and snappy mid range i tried a 21p the same but it didn't increase or lose the top speed but made it feel lethargic on pick up

And performance is pretty much expected:
115hp efi only 36 knots

Originally Posted by beerbelly

my humber 5.5 with mariner 115 and a 19p four blade alloy is hitting 6k at 37 knots .i have tried a 21p but it didn't improve top end and i couldn't get over 5.5k revs plus it had lost any mid range punch . mine is the newer 2.1 liter and has the command thrust gearbox though so different final drive

It must have been ventilating raised 1.1/2" before fitting the four blade? Did you drop it two holes or one?

Lifeboatman is doing the right thing raising his.

[Limecc]

Originally Posted by Limecc

It must have been ventilating raised 1.1/2" before fitting the four blade? Did you drop it two holes or one?

Lifeboatman is doing the right thing raising his.

I can answer part of my own question, you lowered it two holes. Raising 3/4" (one hole up) sounds like optimal.

Honda or Solas equivalent of your Spitfire prop would seem the way to go. Tried and tested, no lean.

[mikehhogg]

One of the most often overlooked causes of Chine Walking is play in the steering, even a tiny bit of play anywhere in the steering system at the speeds you are talking about could cause this effect.