GH 26 Keel question

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JFJ
Posts: 10
Joined: Tue September 6th, 2016, 12:07 am

GH 26 Keel question

Postby JFJ » Fri October 28th, 2016, 12:29 am

Hi all

Well, a chunk of Sampson post is off for a rebuild/refabrication....

Looking at it, I think I should have built it myself, but never mind...

Question for this post, though, and perhaps some eventide's could help here too!

I have recently got my hands on 10 planks of , 20 year old Iroko - strange planks 3 inch at one end, 5 at the other - 1 1/2 inch thick, 7.25 feet long, used as some form of decking for a few years then stored in a barn for the last 5....
They are sun-bleached (never painted), but the first planed down to fresh and looks great, with no rot anywhere (though a few odd bolt-holes ;) )

anyway,

After my adventures running aground, Iris had lost some of the fibreglass with flow coat on the keel bottom. There seems to have been a sacrificial strip fitted, as some has come away quite easily, revealing fairly pristine epoxy skin beneath, suggesting it was added after the construction....
I was thinking of epoxying some of these planks to the keel (and bolting to the bilges, to keep the ratios the same). Obviously, faired to the profile, and to make them at least somewhat hydrodynamic....

I was wondering if anyone had made 'beaching shoes' for a GH or eventide, for tidal rock shore protection, and noticed if the extra depth to the keel with no more weight made any difference to the leeway? I am not worried too much about the increase in whetted area - this will be relatively small... I already have the boat jacked off the trailer, to start stripping the old fibreglass & flocoat so it shouldn't be a big deal to add this.

some thoughts would be nice - good idea haven't seen that on a gh before, done to death, or don't do it!

PS, one of the timbers is a marked man already, for a new staysail boom, and a tiller extension.... Might use another few for the fancy-pants Fiddlers Green rudder setup - but thats next year - probably!

Regards
JFJ
Iris of Glenarm

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Fiddler's Green
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Re: GH 26 Keel question

Postby Fiddler's Green » Mon October 31st, 2016, 9:52 am

Hi JFJ,

Fancy pants here!

The idea of sacrificial iroko under the GRP is not a new one and as you have already found on Iris, many fitted them. A very good idea I would have said.

I have a cast iron ballast keel so it does not need protecting, but almost every year when hauling out I notice the antifouling has been worn away from the bottom, because I often tend to ditch crawl and will gently run onto the mud or sand.. (normally on a rising tide!).

I would be concerned if the bottom of my keel was GRP. I have seen GRP keels worn through!

Good move to add it to the bilge plates too as otherwise you could settle at an odd angle on hard sand etc. Fixing to the bilge plates may be a little more difficult.... but possible.

As for altering the sailing efficiency, every little helps as they say.! Cannot do any harm to add a little to the keel depth, though I do not think it will transform her to an Americas Cup contender!

Do send the pics in when you are doing it!

Regards,
John williams
Proud owner and builder of 'Fiddler's Green'

GHM
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Joined: Thu March 10th, 2011, 9:36 pm

Re: GH 26 Keel question

Postby GHM » Tue November 1st, 2016, 6:39 pm

Hi JfJ.

The idea of a sacrificial GRP (polyester) grounding strip was almost certainly put on your boat by Terry Erskine. I did the same on almost all of the 5 GH31's and the one GH26 I built and found it very satisfactory. That seems to have been borne out as you found pristine gel coat underneath. On my second 31, GH 252, it lasted over 10 years and as far as I know it's still going strong. I regularly dried out ( but tried not to do it on rocks!). My mooring was in the Wareham river and I regularly sat on the bottom between tides. I've done the same on my current GH and always said it would just replace it if needed. Never has been. It's quick and cheap and easily replaced if need be. Never added anything to the bilge keels to compensate for the extra half inch or so. It seemed to dry out the same as my first GH which had an iron keel.

We developed a technique after some experimenting and, in the end, my laminator could apply a strip about 1/2" thick, all along the keel and about 3" up each side, and gel it over in less than a day. But there is a knack to make sure it doesn't sag and fill with air pocket, or worse still, it gets too heavy while it's all still wet, and slowly all slides off. It makes a mess! I won't bore you with the tricks here unless you want to do it, in which case, I'll be glad to advise.

Re attaching other things (wood, metal) we thought about it long and hard. Unless you use buckets of epoxy I don't think that will work and epoxy doesn't bond too well with polyester anyway. I would use one of the decent marine sikaflex polyurethanes. Much simpler, quicker and cheaper. After all, if they can stick a 45 foot hull and deck together without any mechanical fittings, it should be up to it.

We thought about metal and, although I know of one GH which fitted a hefty steel plate, I believe they had to drill well into the hull, which put me off.

I personally wouldn't mess around too much with the bilge keels. You might end up with a result you don't want. I made a few "streamlining" mods to the GH31, thinking that, as an Aeronautical Engineer with quite a bit of experience in fluid mechanics, I knew what I was doing. However, just rounding off the square front edge to reduce drag, resulted in increased vibration at speed.
Best of luck, whatever you decide. Let us know how you get on.

JFJ
Posts: 10
Joined: Tue September 6th, 2016, 12:07 am

Re: GH 26 Keel question

Postby JFJ » Sun October 8th, 2017, 9:25 pm

Hi All

Just hauled out last weekend, and am pleased to report that GHM was absolutely SPOT ON - I built a grounding strip out of some old (20 year old) 2 inch Iroko, and 'glooped' it to the bottom of the keel with 3 tubes of something called 'PU18 - https://www.amazon.co.uk/s/ref=nb_sb_no ... words=pu18 - Polyurathane adhesive I have used for years with great success.
I had a small grounding this year (in mud, intentional), and by the end of the year, I inspected the planks, and everything was sound.

I didnt put anything on the bilge plates - so I list a bit further when I ran agound. No big issue, but my trailer is a bit off, and marked the wood rubbing strakes on 1 side....

Finbar


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