Small crack in hull coating just ahead of bilge keel Trident 24

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kgwanchos

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Hi all

Just doing some work on Greylags bilge keels, about to paint with POR15 as they are flaking fast. She is a Trident 24 centre plater Ive noticed a small hairline crack bout 5 cm long in front of one of the keels with a slight rust stain around it. Last year I coated the hull in 6 coats of gelshield 200 and I do recall coating a small crack just short of 1mil wide and 1 cm long very close to the leading edge of the keel. So obviously this area must be flexing as the boat is pulled up the beach on skids every year hence the gelshield has cracked in this area. Most worrying perhaps is the rust stain. I have no idea what the internal structure of the bilge keels are, I would assume the two keels are one piece with the hull moulded around it ?? Anyhow has anyone had similar and how concerned should I be ? Can I just try and patch it up to stop the water going back in and if so what with ??

Any advice greatly appreciated

Thanks in advance

Karl and Lorna in Corwall UK
 
Hi Karl,
you could just open up the crack a little then fill with an epoxy filler and see what happens.
But I would check inside the hull to see if there is any internal damage. If as you suggest, the keels are flexing, you will need to reinforce the area around the keels with several layers of glass and epoxy. The rust stain may be from a backing plate, which would mean that water is penetrating through the hull.
 
Thanks so far guys.... I am a member of the Trident group and have posted this message there too... just wanted to get a range of opinons here as well. Im just pretty amazed that a bilge keel supporting 3 1/2 tons could be basically bolted to the fiberglass hull rather than just be one piece ! Im getting no water inside the hull as such so I assume Swinranger that it could be getting under the gelcoat but not the substrate ??
 
I'm just stripping antifoul from a Prelude19 bilge keeler.
This is the area ahead of the keel. The cracks are just where the keel foot sits in the moulded recess. Is this the sort of thing you are talking about? There's bound to be a bit of rusting from behind the foot, but unless there is something to make you suspect the keel bolts are corroded I wouldn't worry.

Grp hulls do flex, but large lumps of cast iron don't, so it may be the hull flexing rather than the keels trying to break off.

preludekeel.jpg
 
I dont think the centre plate Tridents had bilge keels as standard. On triple keelers like mine, the plates are moulded in to a housing which extends up under the berths and is very solidly braced to the hull. I know of one where a plate has become loose, but do not know how serious this was (see TOA forum).

If your centreboarder has had bilge keels added, then how serious your crack is will depend on how they are attached. But if a crack is appearing on non-standard keels, then it suggests the hull moulding is being overstressed at that point, and needs some reinforcement to spread the load, either internally or externally.

Any chance of some pics?
 
now that you mention it Old Harry, you're right the Trident manual shows the dropkeel with no bilge keels! So I don't know if this is a bilge keel with added dropkeel or a dropkeel with added bilge keels. But I can't imagine anyone would go to all the trouble and expense of adding bilge keels to a boat of this type and it certainly looks like it was moulded with the original hull. I will get down to the boat yard tomorrow if possible and take a few pics. Many thanks for your help so far.
 
open a free album on photobucket, and upload pics to photobucket from your computer. When the pics are on photobucket, underneath each thumnail pic are a set of links. Click on the one marked IMG, and it will automatically copy it, and you can paste that code on a post here
 
It wouldnt be all that difficult to add bilge keels to a drop keel Trident, and would ensure she sat upright on a drying mooring. I have seen several boats (not Tridents) where this has been done succesfully to avoid long waiting lists for costly deep water moorings in the Solent area, so quite possibly yours has had 'the treatment'. Round here a deep water mooring can cost 1/3rd the value of a Trident, and a Marina berth can be half the value each year, so that sort of mod is often a much cheaper option!

Posting pics is dead easy, as Brendan says, once you have a Photobucket account. One click to upload your pic, another 2 clicks to copy/paste it to the forum.
 
Ok thanks all here are the pics sorry none of the crack but hopefully description above is clear. Its not like yours there Lakesailor there isnt really a foot to that extent the metal only extends about 1cm around where the keel enters the GRP so a very narow foot if you like. Thanks for the explanation oldharry maybe you are right I just would have thought it wouldnt have been possible to add the keels so cleanly after initial build. I will ask on the Trident Forum to see if anyone else has one !
Picture011.jpg

Picture025.jpg

672.jpg

Picture010.jpg
 
Your bilge keels seem to have just been bolted on through the hull bottom. Suggest you look inside to see whether the hull has been reinforced. Drying out on that sort of keel would put a lot of wracking strain on the hull, and would guess that is what is causing the damage. Normally there would be a long stringer bonded in the spread the load fore and aft and probably some transverse floors to take lateral loads.
 
Karl,
looking at the photos I would have expected to see a flange between the top of the bilge keel and the hull to spread the loads a bit. There should be a lot of reinforcement inside the hull in the area where the keels attach, if there isn't you will have problems with hull flexing and cracking.
 
Yes I agree swinranger .... there must be reinforcement somewhere.... they have obviously been on there for some time.... will go down and check tonight and report back with more pics maybe......
 
On the bilge/triple keel trident the bilge plates (deeper than yours) go through the hull into the under berth locker space where they are bolted to a fore/aft mini bulkhead which is then glassed over and to cross bulkeads. This is an incredibly strong arrangement but can be mistaken fo a simple fore/aft divisin of the locker or floor area. There is no flange on these plate keels as is usually the case.

This is from memory of when I owned a triple keel Trident back in the early '70s so I hope my recolection isn't wrong.
 
Yep thanks robin Ive just had a good heads up from someone at the Trident Owner site. Apparently Greylag may well be completely unique in being a centre boarder with bilge keels but they are definately original bilge keels. They even provided me with engineering diagrams with cross sections ! the upshot is I just need to expose the crack and fill it then keep an eye on it

Many thanks to you all for pitching in as usual
 
Here are 2 Triple keel Tridents:

Bob Doe's 'Lottie'

P1010180.jpg


and my 'Spin' (in sold -as-seen condition!)

P4160031.jpg


It seems to me that the keels are deeper than yours, which suggests they were added later, except that they appear to have the standard Trident mounting which takes the plates through the hull, and in to a flange under the saloon berths, which is then braced outwards to the hull, dividing the underberth space in to compartments.

If yours has that arrangment then they are likely to have been standard from new. If so, you need to check internally very carefully for any signs of movement or cracking inside around the plate support structure. If there is none, I would think you can clean out the crack, fill it with epoxy, and wait to see what happens. If it re-appears then you have a problem and would be best to get a surveyor or boat builder to give a second opinion.

Looking closely at yours they have the standard 'shoe' upturned at the fwd end which features on most Woolston built Tridents, which suggests they are original.

In my opinion of course!
 
Thanks oldharry, I have been talking at length with Bob Doe about how it all works and I am now happy they are standard Keels albeit a cut down shallower draft version. All checks out ok internaly luckly so I will just fill and watch. Incidently I made a note of something you mentioned a few weeks ago regards putting some balast up front. I havent been able to sail Greylag at all yet (lots of retoring AND a first baby coming) but I will bear it in mind altho I cant remember why you had to do it now !!

Many thanks again

Karl
 
The Trident was originally designed as a centre-boarder and the bilge keels (and fin keel version) were an afterthought. But the designer Alan Hill did nothing by halves and as these were some of the first GRP boats to be produced (the Trident was launched at the same boat show as PBO in the sixties) they were massively strong compared with today's flimsies.

The 1/2" in galvanised steel bilge plates were jacked up into 3x2 oz csm grp mouldings inside the hull and bolted through with 4x ss 1/2" bolts. These mouldings were reinforced with transverse webs and a longitudinal 7/8" ply reinforcement over 7 feet long which passed through the main and aft bulkead. The whole was then was glassed over again on both sides of the plate with a further 2 layers of 2 oz csm. So the Trident has 10x2oz layers of chopped strand mat , steel plate and 7/8" ply creating a beam 1.5" wide x 9" deep down each side of the saloon and a bilge like an egg box that is massively strong. This is in spite of the fact that unlike most bilge keelers the main weight of this triple keeler boat is not normally carried on these bilge keels (they are in fact shorter than the central ballast keel). Their purpose is just to hold the boat upright when it sits on that ballast keel.

In my view the most likely cause of the cracking is that this section of the hull is so stiff that it creates a hard spot unable to flex with any movement in the hull forward of this reinforcement - just as some boats show gel coat crazing in the vicinity of internal bulkheads.
 
Bob's assessment of the problem sounds pretty fair to me, as he says the keels are heavily over-engineered by modern standards and I suspect mine would bend before the GRP fails.

Ballast up forward is mentioned in the TOA Handbook P44, and gave me the clue that solved a nightmarishly skittish helm. Let go the tiller for an instant and the boat would whip round so fast that it would throw me off my feet! With all that weight aft - including my own not inconsiderable bulk - she was badly out of trim and as I am single handed most of the time, it could be quite dangerous as I felt I never really had her under proper control.

I had not filled the quite large water tank under the forecabin berths, and did not realise until I read Des Sleightholms 'Inside Ballast' article that the boat needs weight up forward to keep her in trim. I added around 150lbs of sandbags under the berths fwd, which with the tank full as well is really a bit too much. The boat now handles beautifully, remaining under full control - errrm, well, most of the time anyway!
 
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