Am I exagerating or this engine is still too low?

[Last Tango]

Originally Posted by jeffstevens763@g

I ve always gone for equal balance throughout the boat which ever boat I own never had any problems I stick with the cav plate level with the keel and trim up to suit and my boats run level. I think your engine is too high as I see it and you need to put weight up front if needed instead of people where it's the roughest ride. All in my opinion of course

Probably setting the engine cav plate a bit lower will help as it lifts the bow but moving weight forward will undo that benefit and make things worse again.
Only two thing cause this 1) Trimmed out too far & 2) Centre of gravity too far forward.
The centre of gravity is already too far forward and that's what's causing the problem.
100% guarantee.....move weight aft, trim down or both....problem solved.

[eze]

Originally Posted by Last Tango

Probably setting the engine cav plate a bit lower will help as it lifts the bow but moving weight forward will undo that benefit and make things worse again.
Only two thing cause this 1) Trimmed out too far & 2) Centre of gravity too far forward.
The centre of gravity is already too far forward and that's what's causing the problem.
100% guarantee.....move weight aft, trim down or both....problem solved.

If I read correctly, the boat is TILLER controlled.

So without having to stick yer children (one on each sponson, aft) and bare arse over the transom the weight is pretty much 'aft'

Accordingly I have to ask how much more weight can be 'aft?'

the conversation seems to be 'aft' but for a tiller control it don't go much more 'aft' than that!

thanks

eze

[eze]

Quote Savard '). I did it in order to improve the general handling, to increase wot speed and most importantly to reduce porpoising at high speed (mostly when I'm alone in the boat)!'


I agree with Jeff here - move the weight forward.

[eze]

Quote Savard 'The boat is probably purposing at slower speed because there is too much weight towards the bow'


By raising the engine, the porposing has gone from high speed to a lower speed?


What would happen if you dropped the engine height lower than your start point?

[savard02]

I think that I need to post more pictures because I have serious doubt about the hull design. The hull as what I would call a "kind of" integrated trim tab...

It's difficult to show it clearly with pictures so I tried my best to make a drawing to explain it .

1st pic: drawing
2nd: from transom looking forward
3th: from transom looking forward
4th: underneath looking toward transom
5th: from transom looking forward (don't judge me on the creepy hand in the background, it's Halloween decoration )

This 'integrated trim tab' must have a huge impact on the general hydrodynamic of the hull. But I can't explain it myself! You guys might be able to understand what was in the head of the hull designer???

[savard02]

Originally Posted by eze

If I read correctly, the boat is TILLER controlled.

So without having to stick yer children (one on each sponson, aft) and bare arse over the transom the weight is pretty much 'aft'

Accordingly I have to ask how much more weight can be 'aft?'

the conversation seems to be 'aft' but for a tiller control it don't go much more 'aft' than that!

thanks

eze

You're right, it's a tiller handle boat.

At first, I had the fuel tank, the battery and myself located 'stern'. I moved the fuel tank and the battery to what I think is just a tad in front of the middle of the boat hull to get a better balance.

So far, the new engine height is the best result I had so far with the boat. But it's kind of scary to go from a purposing boat at cruise speed to a stable boat at WOT.

I played a bit with the "type 27 battery" ~25kg from aft to bow without significant improvement at cruise speed...

[jeffstevens763@g]

looking at your picture is hard to visualize and to me it looks like you have a similar hull to my old quicksilver 500 pilothouse which is a medium v hull with a large planing pad starting well forward as a point working back to the maximum width which on mine was around 12 inches.i will say my boat was a bitch on the plane it sits on the pad at the stern and any movement,bad balance or side waves made it roll around to the point i had to fit auto trim tabs it was as if it wanted to roll over made worse by the height of the cabin.it took me a long time sorting kit out to get the balance right not sure if that helps in anyway but mine was a very temperamental hull.
for info my engine was fitted by the dealer straight on top of the transom.

[Last Tango]

Originally Posted by eze

Quote Savard '). I did it in order to improve the general handling, to increase wot speed and most importantly to reduce porpoising at high speed (mostly when I'm alone in the boat)!'


I agree with Jeff here - move the weight forward.

The OP is having this problem with his wife and kids, anchor, and 12 galls of fuel all moved forward (200Kg ?). just how much weight would you propose moving there?......300-400Kg?

This is a dangerous, "sticking plaster" way of trying to mask a trim issue that he'll pay dearly for the first time the boat "stuffs" into the back of a wave because the bow is far to heavy.
He should be able to trim it out with the engine with the COG about a third of the way forward of the transom. If that doesn't work I'd look at trim tabs (fixed or otherwise) before I'd start piling ballast, that it doesn't need, into a planning boat.

[Last Tango]

Originally Posted by eze

What would happen if you dropped the engine height lower than your start point?

It will try harder to lift the bow you want to fill with ballast.

[jeffstevens763@g]

LT is right moving weight has to be done properly but he needs to go back with the engine height with the cav plate level with the keel then trim the boat and go from there.IMO

do the scuppers drain the deck or the hull?

[babbot1]

Put a set of smart tabs on. My AB porpoised like crazy with the stern heavy boat when I was by myself. The previous owner even put sandbags in the bow locker because the original tabs were broken. EESH.
Easy installation and totally eliminated porpoising. Also helped with hole shot and jumps out of the water. I was amazed at the results.

[eze]

Hi there Savard,


Which model of airsolid do you have;


Does it just have the bench seat in front of the tiller?


If so, then does it ride with no porpoising when family are on the bench seat?


Do you have any gps speed figures;


1 - with you alone at tiller


2 - with you at tiller & bench seats occupied.


thanks
eze

[savard02]

It’s an Airsolid 15 with a fiberglass hull. Can’t find it on the manufacturer website anymore.

I attached some picture but I don’t have any good picture of the deck.

[Last Tango]

Power trim/tilt ?

There'll be gasps of horror at this suggestion as plainly from previous discussions people have had mixed effect from them, but Doel fins are cheap, easy to fit and removable if they don't help.
My personal experience of them on various boats range from "no difference whatsoever" to "instant solution to an issue".
I'm aware that others have had less favourable results but it's a cheap, simple solution if it works.

[beamishken]

Originally Posted by Last Tango

Power trim/tilt ?

There'll be gasps of horror at this suggestion as plainly from previous discussions people have had mixed effect from them, but Doel fins are cheap, easy to fit and removable if they don't help.
My personal experience of them on various boats range from "no difference whatsoever" to "instant solution to an issue".
I'm aware that others have had less favourable results but it's a cheap, simple solution if it works.

I was waiting for someone to suggest these as I didn't want to be the first to get a public thrashing first but I fitted a set to a boat with a similar set up to yours and similar problem and doel fins cured it.
People are inclined to slag them off but my problem was a heavy engine sat high on the transom of a light boat and the fins just added enough lift to stop the porpoising
The usual complaint is they slow down the top speed but mine starts to chine walk flat out anyway so I dont want to go any faster anyway

[jeffstevens763@g]

Originally Posted by Last Tango

Power trim/tilt ?

There'll be gasps of horror at this suggestion as plainly from previous discussions people have had mixed effect from them, but Doel fins are cheap, easy to fit and removable if they don't help.
My personal experience of them on various boats range from "no difference whatsoever" to "instant solution to an issue".
I'm aware that others have had less favourable results but it's a cheap, simple solution if it works.

For £20 ish it's worth a go not a fan myself but if it works spot on, I think you can buy them that don't need to drill the cav plate so no ugly holes if they don't work

[gtflash]

There’s a lot of theory cut and paste from other forums above. In short all boats are unique and should be treated that way. Changing engine height can change everything.

Simple techniques to eliminate porpoise could be moving weight fore or aft. Who cares as long as it fixes it. Depends what your after. If it’s a family boat more weight forward is probably more practical or somewhere in the middle for a neutral trim as Jeff suggests. If you are looking for speed then weight the boat aft more and stability will be reduced. Once you get over 60mph the slightest change in weight, engine height, prop or trim becomes much more noticeable than a 40mph boat.

Maybe you were just driving your boat like you did before and you needed less trim or maybe even more (more likely less). Get some more seat time before spending money. In my experience which isn’t massive the higher the engine the more neutral a trim you need. It eliminates the need for lots of trim out as the thrust line is higher. On my boat higher engine height also reduced Porpoising and torque lean.

Your hull shape could be contributing to the Porpoising. It’s got hook built into it which will lift stern and lower bow. It’s important to remember everything is a compromise on a boat and a boat design. I run my prop shaft level with bottom of hull, but it means I need to feather the throttle to plane. And I need a bit of tab to keep the nose down when kids are on board.

I wouldn’t add a jackplate. I can sell you one if you want. 5.5”setback but it can interfere with trimming up as steering and bits of engine clash with transom unless you go 8-10 back.

Remember lifting an engine lets an engine rev more so ultimately you might need to change the prop or add a blade. It’s a very black art. And one I certainly haven’t perfected enough to definitevely tell others what’s right or wrong. Experiment and have fun doing it but it might be costly. If it ran right before stick it back down and live with it Unless your racing.

[savard02]

Originally Posted by beamishken

I was waiting for someone to suggest these as I didn't want to be the first to get a public thrashing first but I fitted a set to a boat with a similar set up to yours and similar problem and doel fins cured it.
People are inclined to slag them off but my problem was a heavy engine sat high on the transom of a light boat and the fins just added enough lift to stop the porpoising
The usual complaint is they slow down the top speed but mine starts to chine walk flat out anyway so I dont want to go any faster anyway

Well, I'm not completely closed to the idea of having a doel fins installed but I would rather go without. I want to make sure that every other issues are addressed before going there.

The one who doesn't involve drilling of the anti-ventilation plate are expensive and seems to be targetting bigger engines than mine.

I am keeping that option in my back pocket in case everything else fails! But hey, I gonna have to learn to love it because right now find them very ugly!

[babbot1]

Don't do the doelfin / whale tale. Trim tabs or smart tabs will work much better. Check out Nauticus trim tabs and get the proper size for your boat. You can get them on Amazon.
Completely eliminated porpoising for me. They work as described (for once)

[Last Tango]

Originally Posted by babbot1

Don't do the doelfin / whale tale. Trim tabs or smart tabs will work much better. Check out Nauticus trim tabs and get the proper size for your boat. You can get them on Amazon.
Completely eliminated porpoising for me. They work as described (for once)

That is complete overkill (as is jackplates and the like) for the OP's problem and will cost five times the price!

Porpoising is the result of a fairly minor trim issue that doesn't take much to sort and I'd rather be drilling 4 X 6mm (easily re-filled) holes in the cav plate than drilling into the transom.

The Doelfins will completely eliminate the issue and they can be adjusted with the engine's trim to suit the boat speed. I've fitted fixed trim tabs to boats before and on both occasions they solved a low speed planning issue and created a ploughing problem at high speed.

As gtflash says. You might have to move the engine back down as well to sort this but I'd just get a set of Doel fins (for all they cost) and give it a try.