Ballast and Hydrofoils

Johnny_Canada · 02 February 2022, 15:14

Hello RIB Community!

I'm trying to solve a balance problem. My Highfield Sport 460 w/Yamaha 90 porpoises in its natural state, and it pulls hard to starboard when at half throttle or more. So I added a foil, and adjusted the torque tab to point full starboard.

That solved both problems, but introduced a new one: now when under speed, as the foil starts to lift the hull a list to starboard develops. When approaching full throttle, chine walking creeps in. As this RIB has a starboard helm position, I'm going to try ballast (sandbags) under the port side of the rear bench.

Has anyone else experienced this issue? If so, any other insights or suggestions would be welcome!

Pikey Dave · 02 February 2022, 15:25

My first thoughts are that the engine is set too low.

Johnny_Canada · 02 February 2022, 16:16

Thanks Dave. When I took delivery of the boat, I checked to ensure the cavitation plate was lined up with the keel, but I'll have another look. My last boat had the opposite problem, so it's possible my eye was too generous.

beamishken · 02 February 2022, 18:19

Quote:

Originally Posted by Johnny_Canada

Thanks Dave. When I took delivery of the boat, I checked to ensure the cavitation plate was lined up with the keel, but I'll have another look. My last boat had the opposite problem, so it's possible my eye was too generous.

Very few boats run optimally with the av level with the keel I usually start by mounting about 1" above and go from there. As pd says sounds too low

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Limecc · 02 February 2022, 20:04

That's really odd. A RH rotation prop should steer or lean it to port (left).

GuyC · 02 February 2022, 20:22

When you say it pulls hard to starboard, do you mean it turns to starboard or lists to starboard?

I think the forward end of the torque tab should be to port of the centreline to correct the torque list on a RH prop. If it is adjusted too far, would it cause a stbd list.

jeffstevens763@g · 02 February 2022, 20:41

Use drums of water so you can fine tune it if all else fails easier than sand bags.

Searider · 02 February 2022, 21:36

90hp on a 4.6m boat is "a lot"

Orwell boy · 02 February 2022, 22:22

Quote:

Originally Posted by Searider

90hp on a 4.6m boat is "a lot"

Wise words i think ,i had a 2014 highfield with a max hp mounted and was rated 90hp . the 4.6 was a narrower beam i believe reckon max was 60hp

beamishken · 02 February 2022, 22:32

A deep running engine on a boat potentially maxed out or maybe overpowered fitted with doel fins & a steering fin at full deflection is going to do weird things.
Address the height first & probably remove the doel fins which it shouldn't need with that power & it should start to improve imho
Start to jack the engine up one hole at a time untill it starts to ventilate excessively then drop back one hole & your about there

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Limecc · 02 February 2022, 22:46

Quote:

Originally Posted by Searider

90hp on a 4.6m boat is "a lot"

Absolutely. We don't know which make but a Suzuki 90 is 155kg and then you've got the rear bench seat arrangement, so potentially two adults combined, the same weight again some 300kg all at the stern of a 15ft boat. That's almost the dry weight of the hull. Where's the 55L fuel tank?

No wonder you fitted the hydrofoil. Compromised unbalanced design seen also in the smaller Brigs.

Ken's spot on about the engine height. It's low at the stern like my 15' boat and I was able to get the engine AV plate 1.1/2" (2 holes) above keel which is perfect and just as well because I ran out of further adjustment. I tried running without the hydrofoil but soon put it back on and I haven't noticed any ill behaviour from it at high speed*.

Out of interest, at WoT can you trim up the engine so the prop ventilates? This was impossible on mine until the engine height was optimised, because the flow of water above the fin was stronger than the hydraulics.

** Also mine porpoised until I lifted the engine. Probably because the fin was too low. Haven't got that issue now but to be fair it only happened once when testing on a pancake flat river, it was quite pronounced.

Limecc · 02 February 2022, 23:54

Quote:

Originally Posted by Johnny_Canada

My Highfield Sport 460 w/Yamaha 90

Yamaha 90 = 162kg. Even worse than the Suzuki

Johnny_Canada · 03 February 2022, 03:59

Thank you all for your thoughts, suggestions, ideas, and questions. This is all tremendously helpful. The consensus seems to be to check the mounting height of my (far too big for this boat) Yamaha again, and try adjusting upward.

To answer some specific questions that came up:

Guy - I mean the boat turns to the right, and hard, if I take my hand off the helm while under power. The problem of a list came later, after installing the foil. Although the foil solved the turning to the right problem; I could take my hand off the wheel and she would run true. Regarding the torque tab, you are correct - the forward part of the tab is pointed to port, with the rear pointing starboard.

Jeff - Good idea to use water instead of sandbags. Until I can raise the motor, I might use a combination with the water being what I think will be the 30-40lbs of variable weight I'll need to adjust as I dial it in.

Searider - yeah, agreed. 90hp is a lot on this boat. On a do-over I would put 70 on her and call it a day.

Ken - good suggestion. I've already taken the fin off for now while I've been trying to solve, and will leave it off while sorting out the mounting height. You've got me wondering if I should install a jack plate so I can make multiple adjustments as needed until it's right.

Limecc - the fuel tank runs along the length of the hull, below the deck. You're also bang on with your assumptions about how ass heavy I am when underway with 2 adults on the rear bench, sitting on a locker full of the day's essentials. To your question about trim, no I can't get it to ventilate. I do have to trim it very high (with the fin installed), so any higher and the prop would just come up out of the water.

Thanks again to you all.

Cheers,

John

Limecc · 03 February 2022, 07:15

Quote:

Originally Posted by Johnny_Canada

To your question about trim, no I can't get it to ventilate. I do have to trim it very high (with the fin installed), so any higher and the prop would just come up out of the water.
John

What I'm saying is I couldn't get the prop to ventilate by trimming up out of water. It would only go so far. You obviously can. It was only possible without hydrofoil.

When you've sorted the issue you might consider fitting NFB steering. It's cheap enough unless you go hydraulic.
You shouldn't ever be able to take your hand off the helm under power btw. Mine would steer hard to port with a neutral trim tab. Do you have a photo of the prop? Also shame you can't post a pic of the fin. It might have been misaligned.

Also did you know you can lift the engine at home using just the trailer and jockey wheel method?

beamishken · 03 February 2022, 08:58

Quote:

Originally Posted by Johnny_Canada

Thank you all for your thoughts, suggestions, ideas, and questions. This is all tremendously helpful. The consensus seems to be to check the mounting height of my (far too big for this boat) Yamaha again, and try adjusting upward.

To answer some specific questions that came up:

Guy - I mean the boat turns to the right, and hard, if I take my hand off the helm while under power. The problem of a list came later, after installing the foil. Although the foil solved the turning to the right problem; I could take my hand off the wheel and she would run true. Regarding the torque tab, you are correct - the forward part of the tab is pointed to port, with the rear pointing starboard.

Jeff - Good idea to use water instead of sandbags. Until I can raise the motor, I might use a combination with the water being what I think will be the 30-40lbs of variable weight I'll need to adjust as I dial it in.

Searider - yeah, agreed. 90hp is a lot on this boat. On a do-over I would put 70 on her and call it a day.

Ken - good suggestion. I've already taken the fin off for now while I've been trying to solve, and will leave it off while sorting out the mounting height. You've got me wondering if I should install a jack plate so I can make multiple adjustments as needed until it's right.

Limecc - the fuel tank runs along the length of the hull, below the deck. You're also bang on with your assumptions about how ass heavy I am when underway with 2 adults on the rear bench, sitting on a locker full of the day's essentials. To your question about trim, no I can't get it to ventilate. I do have to trim it very high (with the fin installed), so any higher and the prop would just come up out of the water.

Thanks again to you all.

Cheers,

John

The doel fin will help with the porpoiseing but for height testing and straight line running tests its better off removed. Lifting the engine is easy, just loosen the lower bolts part way and pull out the top ones you can trim down onto a wood block to support the engine and lift the jockey wheel to slide the motor up the transom to the next set of holes its a 10 mins job & you can try several heights at the slip in an afternoon.
Dont worry too much about sealant at the slip you can pull the bolts out later 1 at a time to re seal the holes

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Johnny_Canada · 03 February 2022, 15:56

Quote:

Originally Posted by beamishken

The doel fin will help with the porpoiseing but for height testing and straight line running tests its better off removed. Lifting the engine is easy, just loosen the lower bolts part way and pull out the top ones you can trim down onto a wood block to support the engine and lift the jockey wheel to slide the motor up the transom to the next set of holes its a 10 mins job & you can try several heights at the slip in an afternoon.
Dont worry too much about sealant at the slip you can pull the bolts out later 1 at a time to re seal the holes

Sent from my SM-G950F using RIB Net mobile app

Thank you for this - I was over thinking how difficult it would be to raise the motor and thought it would have to be a dealer item. Also, I agree about the fin. Better to solve this without accoutrement, I can always reinstall the fin later.

Johnny_Canada · 03 February 2022, 16:07

Quote:

Originally Posted by Limecc

What I'm saying is I couldn't get the prop to ventilate by trimming up out of water. It would only go so far. You obviously can. It was only possible without hydrofoil.

When you've sorted the issue you might consider fitting NFB steering. It's cheap enough unless you go hydraulic.
You shouldn't ever be able to take your hand off the helm under power btw. Mine would steer hard to port with a neutral trim tab. Do you have a photo of the prop? Also shame you can't post a pic of the fin. It might have been misaligned.

Also did you know you can lift the engine at home using just the trailer and jockey wheel method?

Ah, thanks for clarifying re: ventilation. Interesting idea about the NFB steering, I'll give that some thought. Thanks also for the suggestion of using the trailer/jockey wheel method to raise the engine.

Just to clarify that I'm not blasting around the waters of British Columbia hands free from the helm - when I take a hand off the wheel it's for a split second, with my hand hovering directly above just to see what the boat wants to do left to it's own devices. I know you aren't suggesting I'm being foolish, but want to be clear nonetheless!

Here's a pic of the prop and fin. Hope it uploaded correctly.