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Old 13 May 2023, 19:42   #1
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Broken Keel Board

Had my new Volante 390 and Tohatsu 20hp out for it's maiden voyage today.
Whilst inflating the keel, I heard a loud crack from the front keel board.
Suspecting it was damaged, I still launched and had an hour on the water to get some engine hours.


As soon as the boat got up to planing speed, the cavitation I was getting was awful.


When packing the boat away after my session, the keel board had clearly snapped, I hadn't even got anywhere near the recommended pressure when it broke on inflation.


A couple of questions, will the cavitation issues be due to the broken board ?.
The ventilation plate is about 1 1/2 inches beneath the keel.


I also had very spurious readings on my Garmin Striker, again, this won't have been helped by the cavitation issues.
The transducer is level with the bottom of the boat.



I'll get onto Excel on Monday for a replacement board.


I have also seen members on here, changing their boards for something stronger, clearly the supplied boards are not up to it.
A few pics are attached for you,

Thanks for any advice you can give.
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Old 13 May 2023, 20:19   #2
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Hi Stu, first and foremost the board needs to be replaced by Excel, I ran over mine with a 2 tonne Navara and it didn't crack is cleanly as that board has.
The cavitation is probably not helped by the snapped keel board but I wouldn't think it is the main issue.
Is the OB sat on the transom as low as possible with no packing? I think most with an Excel find that the best place for the OB is on the transom with no packing. Looking at your picture, the cavitation plate looks to be below the transom but level or above the keel. Did you top up tubes, floor and keel pressures after you had been in the water 10-15 mins? I have found that pressure is really critical on my SD360, and I can only assume it is even more so on the SD390. I now over inflate my tubes, floor and especially the keel by an extra 0.5psi every time before I launch, and then check after 20 mins or so.
Transducer mount looks as though it's on the prop side on your transom wheels, perhaps a little to close to the prop?
If you have room to transport the type of keelboard I made for Redneck, I would seriously take a look at making something similar.
https://www.rib.net/forum/f50/airdec...ign-87561.html
It transformed the way that Redneck behaved in the water.
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Old 13 May 2023, 20:35   #3
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Thanks Steve,
The OB is sat on the transom with no packers so can't get any lower.
I didn't check the pressures once on the water, but they seemed ok.
I'll have a look to see if I can remount the transducer on the starboard side of the wheel.
I think I'll get my replacement board first, and certainly look at the boards you added.
1 1/2" inch distance between the keel and AV plate should be fine, shouldn't it ?
I'll let you know how I get on,
Stu
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Old 13 May 2023, 20:41   #4
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Keep us all informed, especially how you get on with Excel now it is under new ownership.
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Old 13 May 2023, 21:28   #5
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Obviously replacing that keel board is pivotal but then pressures, outboard height, weight distribution and even prop choice make a big difference to air floor SIBs. However cavitation might always be present to some degree with a long air floor model. It’s an offset to their lighter weight and ease of setting up.
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Old 14 May 2023, 05:01   #6
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I have found that pointing the transducer slightly forward (about 2 clicks from level) helps it to hold depth well and not flash
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Old 14 May 2023, 07:51   #7
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Thanks for the replies guys, first job get the replacement board and then I can make a few adjustments to try and eliminate the cavitation.
Looking at my pic of the outboard, would you say it was at the right height, obviously I can't go lower, and raising it would make matters worse wouldn't it ?
My trancducer reads fine when at slow speed, just worsens with the cavitation .
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Old 14 May 2023, 10:48   #8
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Transducer

>>>My transducer reads fine when at slow speed, just worsens with the cavitation


I wouldn't worry too much about about the transducer until you have the main issue sorted as far as possible as then the transducer may be fine. I don't use a depth sounder any more but when I did I just made up a crude but effective slotted wooden mount and trimmed it to a neater job once I'd established the height that worked best. Photo below.

I've echoed the term cavitation in my previous reply as it's been used above but of course this is ventilation you are suffering.

I'd really not worry until you have that keel board replaced and also checked the tube/floor/keel pressures when the boat has been on the water a few minutes as Steve says, it's not enough with a long air floor SIB that pressures "seem right", they need to be accurately measured and up to the max. Also worth asking if you trust the gauge you are using, some are wildly out. I always have two manual gauges plus the setting on my elec pump. As long as all three are near enough the same I'm happy.

Also take care to get an even weight distribution on your next run and trial with an outboard trim position either side of the one you are using at the moment to see if that changes anything.

Knowing how it goes with all that sorted will give you a baseline for further changes or to leave as-is.

BTW for us to judge the outboard height/trim you really need a side on image with a ruler on the AV plate giving a better idea of the level and angle relative to the SIB floor. Having said that it looks between OK and a little low but raising isn't the answer at the moment.
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Old 14 May 2023, 18:18   #9
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Thanks for that, it all makes sense.


When you say try outboard trim position either side of the one I am using, do you mean by moving the trim pin position ?, it's on the lowest setting at the moment.


Or do you mean adjust the engine slightly side to side on the transom mount ?, so it's not sitting in the middle .


I shall address the transducer issue once i have sorted the keel board, I do need an accurate depth sounder because I shall be using the sib for spearfishing trips, as long as it reads at slow speed that will do.
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Old 14 May 2023, 18:56   #10
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I mean the outboard trim pin that dictates its leg position relative to the saddle... how close the outboard leg is to the transom.

You would normally start in the middle hole (do you have 5?) and go from there. With the pin in the lowest position, one that is the nearest to the transom it could tend to drive the bow down causing poor performance and an odd steering/directional feel like a swerving/grabbing.

Moving the pin away from the transom will tend to lift the bow which sounds as if it's what you want.
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Old 14 May 2023, 20:43   #11
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Quote:
Originally Posted by Fenlander View Post
I mean the outboard trim pin that dictates its leg position relative to the saddle... how close the outboard leg is to the transom.

You would normally start in the middle hole (do you have 5?) and go from there. With the pin in the lowest position, one that is the nearest to the transom it could tend to drive the bow down causing poor performance and an odd steering/directional feel like a swerving/grabbing.

Moving the pin away from the transom will tend to lift the bow which sounds as if it's what you want.

The three things which I think will alleviate your cavitation /ventilation problem.
New keel board, pressures spot on (not "seem right") and as Fenlander says OB pin position /trim.
For a bit of a guide, I run my SD360 with a 20hp Merc (practically the same OB as a Tohatsu), 2 up - dog - day kit, in pin position 2 & 3 depending upon the sea conditions. Having the pin in position one (closest to the transom) will not only cause the problems as Fenlander has mentioned, but it will drive the bow down and the transom up causing ventilation.
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Old 15 May 2023, 07:21   #12
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Thanks again, that all makes sense, certainly a few things to change there.
Shifting the trim position away from the transom will raise the bow and drop the stern down a bit which should then possibly help the transducer issues.
I'll let you know how I get on once I have received my new board.
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Old 25 May 2023, 14:22   #13
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Finally received my new keel board from Excel, I was not very impressed with the customer service to be honest.

Initially they wanted me to pay for the board, £ 30 plus £15 p & p. which I refused to accept when the boat was 2 weeks old.

The manager Steve, said he thought that I was an old customer, for some reason I wasn't on the system as having just purchased the boat !!.

Anyway after many phone calls and chasing them up, it was sent out.
Nobody ever rang me back to explain what was,or was not happening.

I don't know what was going on, nobody seemed to know.
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Old 25 May 2023, 14:24   #14
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So, while waiting for the board to arrive, I attached another piece of ply to the cracked board just so I could get the boat on the water .
I am still getting cavitation issues but not until I was up to around 12 knts which I can live with, fast enough for me.
I started with trim hole 3, then 2, I found the best position was I, closest to the transom funnily enough.
I checked the pressures on the water and topped up the tubes accordingly which I think made a slight difference.
I measured 40mm clearance between the bottom of the transom and the ventilation plate using a straight edge.
I am going to attach a 15mm piece of ply to the new board, I feel 12mm is not thick enough.
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Old 25 May 2023, 19:06   #15
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Hi Stu, bit of a poor show from the new owners of Excel. You would think they would fall over themselves backwards giving good customer service trying to improve the reputation from what can only be described lack luster service in the past.
I didn't realise they had gone back to using ply (they did try carbon fibre for a time) but I think your thoughts about using 15mm + 12mm is a bit of overkill for a keel board. I'd make a new board out of 15mm exterior ply, seal it well especially the edges and/or use epoxy resin.
Now to your ventilation /cavitation problem. IMO having the pin in the first trim hole ie: nearest the transom, is going to make the problem worse, as it is driving the bow down, lifting the transom up and probably not getting the SIB on the plane. You obviously can't put the ob any lower on the transom and you say that the pressures are correct (I can't emphasise that enough, especially the keel and airdeck) so that leaves weight distribution. I assume it's just you in the SIB? Is the fuel tank secured towards the bow along with everything else you are carrying? Are you sitting as far forward as you can physically get whilst still having a hand on the tiller? Maybe, think about using a tiller extension.
Excels are very wide, and have a lot of surface contact with the water. I think they take that bit more to get them on the plane. The bow needs to lift naturally, speed through the water, and not artificially by having to much weight to the rear trying to lift the bow. I find it harder in my SD360 to get on the plane when I'm solo, I find it much easier when we are 2 up.
If all that doesn't work, I am sure someone will come up with a solution for you.
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Old 25 May 2023, 20:20   #16
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2 of us in the sib with fuel tank and that's it, no kit.
I know it sounds wrong but the first trim position produced the best ride.
I'm going to buy some 15mm marine ply tomorrow and make an H shaped keel setup like yours.
What thickness you use ?.

I'm sitting on the rear bench seat whilst driving.
Like I said Steve, I am quite happy with what I'm getting at the moment, I can try and tweak a few things later.
My rear board digs into the sides of the boat, when I lifted the boat onto it's side I noticed it, quite a ridge was being created, surely that can't do the material any good.
Did you make your design slightly shorter in width to stop this problem or the same width as the originals ?
I'll get there in the end, thanks for all the info.
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Old 25 May 2023, 21:50   #17
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Originally Posted by sturaffs View Post
I'm going to buy some 15mm marine ply tomorrow and make an H shaped keel setup like yours.
What thickness you use ?
18mm Structural Exterior Grade Ply (don't waste your money on marine ply, there really is no need to use it for a keel board) Should be around £45 a sheet, bought 4 sheets yesterday from my local supplier.
No matter what ply you use, it must be sealed. I used epoxy resin.


Quote:
Originally Posted by sturaffs View Post
My rear board digs into the sides of the boat, when I lifted the boat onto it's side I noticed it, quite a ridge was being created, surely that can't do the material any good.
Did you make your design slightly shorter in width to stop this problem or the same width as the originals ?
I'll get there in the end, thanks for all the info.
Obviously Excel have not taken on board what I pointed out to them when I bought my SD360, take a look at this thread:-

https://www.rib.net/forum/f50/inflat...oon-84238.html

I did make the width of my redesigned keelboard narrower. I think by 20mm overall, however if I was you I'd make it to the width they are now and reduce it by 5mm try it and if its too wide reduce it by another 5mm. One thing which made a big difference was chamfering the edges to try and match the "V" of the "hull".
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Old 26 May 2023, 21:59   #18
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Picked up the ply today and marked it out ready for cutting.
Your pics from your above thread showing the board pushing up against the hull is pretty much the same as I am getting.
I trimmed 15mm off my back board and chamfered it down.
The front board doesn't dig in at all.
I'll make the new board setup to size and like you say, just keep taking little bits of until happy.
Thanks for all your help Steve.
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Old 26 May 2023, 22:35   #19
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Picked up the ply today and marked it out ready for cutting.
Your pics from your above thread showing the board pushing up against the hull is pretty much the same as I am getting.
I trimmed 15mm off my back board and chamfered it down.
The front board doesn't dig in at all.
I'll make the new board setup to size and like you say, just keep taking little bits of until happy.
Thanks for all your help Steve.
No problem, it's what Ribnet is for. Keep us informed about how things go.
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Old 31 May 2023, 05:29   #20
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Originally Posted by sturaffs View Post
Finally received my new keel board from Excel, I was not very impressed with the customer service to be honest.

Initially they wanted me to pay for the board, £ 30 plus £15 p & p. which I refused to accept when the boat was 2 weeks old.

The manager Steve, said he thought that I was an old customer, for some reason I wasn't on the system as having just purchased the boat !!.

Anyway after many phone calls and chasing them up, it was sent out.
Nobody ever rang me back to explain what was,or was not happening.

I don't know what was going on, nobody seemed to know.
Interesting. I also am not very impressed with the new owners. Didnít take to them at the SBS show either
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