Ultimate Trim Tab position

[Dignity]

Previously on my Allison 195 Vision the amount of room under the duckboard meant that I had to use short actuators and the trim tabs ended up around 170 mm from the chine. With the replacement pod there is an increase in height below the duckboard and I now realise that I can move the tabs 70 mm to where the hull flattens 100mm before the chine so that it is still in line with the hull bottom but further outwards.

I'm thinking of moving the tabs for 2 reasons:
1 - all my crew weigh twice my weight and generally the ice and fish are on the same side of the boat so I do have to deploy the tabs quite considerably on that side due to lean. and
2 - when the tabs are deployed they are within 50 mm of the transducer and therefore the reading is sketchy at speed due to turbulence from the tabs

There is some work involved as on the port side there is the live bait pump which will need to be moved and on the starboard side the pick up for the deck wash may have to be moved although I may just get away with some bending of the bracket it self.

What I'm looking for, will a 70 mm outwards movement of the trim tabs give me more control and also less turbulence to the transducer given the amount of repair work needed to the duckboard plugging old screw holes, shifting the bolts/screws holding the duckboards (5 mm left or right and I wouldn't have had to shift these) and plugging the old holes on the transom and repairing the gelcoat.

Or is it a lot of work for little return?

[scottar]

What is the distance from the keel to the centre of the tab now Sam?

Applying a bit of bush logic (correct or otherwise) :-?

You can run some numbers through a torque calculator to see what sort of change the extra 70mm will make percentage wise given a fixed amount of applied force. To my way of thinking, as an example - if the distance was 100cm's and you increase it to 107cm's, you will see a 7% increase in rotational torque applied making the assumption that for any given boat speed the water flow to the tab remains the same thus the amount of force applied is the same.

Calculate Torque from Force & Lever Arm Length (sensorsone.com) (https://www.sensorsone.com/force-and-length-to-torque-calculator/)

[Dignity]

Scott, it is 710 mm from the centre of the hull to the centre of the tab, there is a narrow planing plank which is 120 mm wide which means from the edge of that plank to the centre of the tab is 650 mm. I'll play with the figures as it seems there will be an improvement, even more so with the transducer.

[stue2]

Definitely give you more from the tabs by moving them outboard.
Be a bit of work but you might like the results more

Sent from my SM-G780F using Tapatalk

[scottar]

Assuming my theory holds water Sam you will see close enough to a 10% difference in torque applied to the hull for any given tab position. Hopefully someone around these parts with a bit more engineering nouse can confirm whether this is correct ........or I'm barking up the wrong tree. Whether that's worth it is a decision only you can make mate. What size are your planes?

[Dignity]

Assuming my theory holds water Sam you will see close enough to a 10% difference in torque applied to the hull for any given tab position. Hopefully someone around these parts with a bit more engineering nouse can confirm whether this is correct ........or I'm barking up the wrong tree. Whether that's worth it is a decision only you can make mate. What size are your planes?
Scott, they are 12" x 12", I think I will go ahead, if I can get a better sounder reading it will be a bonus.

[Dignity]

Definitely give you more from the tabs by moving them outboard.
Be a bit of work but you might like the results more

Sent from my SM-G780F using Tapatalk

Thanks Stue although maybe I should get skinnier crew.

[Noelm]

Might pay to have a look over the back at planing speed to make sure there is a clean flow of water further out (there probably will be) but, better to be sure.

[The Mad Cat]

I know the actuator is just sitting on your transducer, but that could be one of those brilliant idea's (the ones you get when the wind is up) to adjust transducer height at different speeds till you get it reading correctly.
Ahh well back to watching the weather report again.

TMC

[Getout]

I think that I would try adjusting the moveable ballast first. Prop torque will always cause heel to port and its worse with trim in. They are big tabs. They should work well enough where they are.

[inveratta]

I have no doubt in principle it will work "better"...the rest is just time and effort!

As far as the transducer goes...I followed a post in here some time ago and mounted the transducer in a wet box inside the transom...as far astern as possible...although I believe there is some loss of signal strength for deep water use ...otherwise its been brilliant..transducer protected ..less clutter on the transom to be damaged etc...less holes on the outside...just a thought...

[Dignity]

I know the actuator is just sitting on your transducer, but that could be one of those brilliant idea's (the ones you get when the wind is up) to adjust transducer height at different speeds till you get it reading correctly.
Ahh well back to watching the weather report again.

TMC

Now that's an interesting idea.

[Dignity]

I think that I would try adjusting the moveable ballast first. Prop torque will always cause heel to port and its worse with trim in. They are big tabs. They should work well enough where they are.
My mate will get of his seat and stand in the centre but on longer trips no such a good for his knees. He's been told by his docs he needs to lose a fair bit of weight but he just keeps putting it on. I don't help with having the pie warmer on board.

[Dignity]

I have no doubt in principle it will work "better"...the rest is just time and effort!

As far as the transducer goes...I followed a post in here some time ago and mounted the transducer in a wet box inside the transom...as far astern as possible...although I believe there is some loss of signal strength for deep water use ...otherwise its been brilliant..transducer protected ..less clutter on the transom to be damaged etc...less holes on the outside...just a thought...

I have thought of a wet box but limited space easily accessible and don't want to put a spin out in the floor at this stage although with the wind coming up it might be another project I could do.

[Dignity]

Project is on hold unfortunately as put a dingle in the bosses car today and she is not happy. Have to repair that first.

[Dignity]

Ok, back onto my project but another snag. Tried to take off the live bait pump bracket and it seems that using plenty of sika or equivalent behind the plate is not such a good idea. It has stuck so well that it pulled the gelcoat off, seems to have a very thin coat there, bummer. The good point is it was dry as a bone there. So a small repair job required.

So now to get the tabs off and the question is what will happen to the gelcoat. Does sika soften if some heat is applied to the tabs with a heat gun, I'm aware there will be a fine line before it starts to affect the gelcoat. Any one tried it?

[Noelm]

I don't think heat will soften it, once it's cured it's pretty solid, I think you are going to have to invent something to cut behind it, like when they cut car windscreens out with wire, but then, if you can try a bit of heat on the pump bracket you just pulled off, you never know.

[Dignity]

I don't think heat will soften it, once it's cured it's pretty solid, I think you are going to have to invent something to cut behind it, like when they cut car windscreens out with wire, but then, if you can try a bit of heat on the pump bracket you just pulled off, you never know.

Might be worth a try with the wire thing. It's just bad luck I suspect that the area the pump bracket was screwed to wasn't so much as thin but the glass hadn't been rolled in properly as the first layer of CSM was white and no resin in sight, a flaw in manufacturing. The boat is just over 30 years old and it's just one of those things that would never shown the light of day until I started playing with it.

[scottar]

My go to is a length of braid between a couple of dowels. Doesn't work all the time and is better if the sika is thicker. Next up is multiple razor blades or Stanley knife blades used like wedges VERY carefully. Last one is a fillet knife - modified with a chisel point if it makes life easier.

[blacklab]

pppppppppppppp

[Dignity]

Thanks for the hints Scott, Col, I guess my 1 day project just got bigger but on the plus side the weather isn't playing ball.

[Dignity]

Ok, just waiting for resin to go off. Finally managed to get the tab off, what a job. The wire thing just wasn't cutting it, I ended up using a couple of paint putty blades and first of all just starting at the edges and tapping with the hammer, going deeper on every pass buy about 1/2 mm, the sealant was that tough, apparently Simpsons Sealant was used on it, certainly much stronger than Sika. I followed through with a much wider putty knife just to keep a small amount of leverage on the tab. Cleaned it all up, cleaned out the screw holes and filled them with resin via a little syringe I have especially for that purpose.
Later on this afternoon I'll have to flowcoat the area, sand it back (painful job at the best of times) buff and polish it. Then I can reinstall the bait pump and trim tabs in their new positions. Fortunately the Starboard side I won't need to move the deck wash pick up as I can cut 5 mm off the tube and it will all fit.
I'm starting to wonder why I started this job.

[Funchy]

Thanks Stue although maybe I should get skinnier crew.


fyi, since starting in the mines I’ve lost weight

hint hint

[Dignity]

fyi, since starting in the mines I’ve lost weight

hint hint

Almost didn't recognise you the other week.:)

[Dignity]

Quick update, got some time today and made the effort to move the port side trim tab. It now allows me a bit more flexibility to move the transducer if necessary and now looking at it as it is not so close to the hull I suspect maybe even a slight improvement in economy which would be a bonus.
I decided to put another project on hold and have now removed the Starboard trim tab, a lot easier for some reason and have injected all the old holes with resin, I'll finish it off tomorrow.
The old position,
124634
The new position
124635

[Mopheus]

have injected all the old holes with resin

Did you have to thicken it first? Have to do similar on mine but worried about not getting all the air out and having the resin just flow back out.

[Dignity]

Did you have to thicken it first? Have to do similar on mine but worried about not getting all the air out and having the resin just flow back out.
Yes I did, I have plenty of Q Cells which I added, not enough to make a paste but just thickened it a bit. The syringe I used was actually one of those Ant Gell (tallon I think) syringes which was all used up, I kept it especially for this purpose. I used some masking tape (the one used for brickwork and concrete is really good) which I secured just below the hole then injected it in and taped it up, even unthickened it won't run out much. There will be a little dimple once set but that isn't an issue, the biggest headache is colour matching the gelcoat afterwards to fill them and other damage to the gelcoat.
The tints I used were yellow and ivory, remember very little is required.
This is where the live bait pump bracket that caused me issues, repaired, flowcoated, sanded and polished and moved to the left by about 50mm.

[Mopheus]

Great work 👍

Yeah I have yet to play with colour matching. I have to match cream, tan and brown on mine. Bought white base for the lighter ones and neutral for the brown, plus cream + tan + brown + black + red + yellow + blue pigments for tinting. Will try to tint batches large enough to do all I need and then just portion out and add MEKP as necessary.

[Dignity]

With the tinting start with just a dab on the end of a match stick, you will be surprised at how little is needed. Only start with enough flowcoat to do the job at hand, keep your base colours clean, I have found the tint will reduce the shelf life and if you over tint you'll have some to add to it.

[Dignity]

Did the starboard side today , went easier after the port side was done. Looks so much better as well, hoping it will work better all around.
Also learnt that beeswax works really well when tapping into ally. I couldn't find where I put it this morning so tried zipper lube and it worked almost as well.

[Dignity]

Last update, had a window of opportunity to sneak out this morning to trial the mods. Winds were predicted at 10 knots northerlies going to up to 20 knots after lunch. New moon was last night so thought they might be on the chew today and Funchy was on his break which worked out well.
I wasn't as heavily loaded as normal but still stuck with weight distribution being the same, have some changes in mind for that. I needed far less port side down which was a blessing and the sounder readings were a little better, I suspect the transducer needs to be further away from the pod. Fuel economy, probs the same but I will check it out over the next few trips.
The fishing was a different story, stopped at the first yellow beacon out of the bar and very quickly loaded up on yakkas and moved out to try for some big grassies and snapper. Fish were showing up everywhere but we could not entice them to bite. Different rigs, jigs SP's, vibes all for nought. Funchy did jag a nice wire netting cod and I did get a few nursery red emperor but even the rubbish fish just didn't want to cooperate. We gave up as the winds picked up quickly and with a falling tide decided to head back across the bar before it got too shallow.
Now for my next project........