Structural GRP question about temperature.

One last practical suggestion is if you are molding extra glass into the bottom and sides of the wells then sand bags may well help apply a force new glass onto the old resin. Wrap the bags in polythene to ensure release from the resin. You might consider puting the sand bags in an oven to get them warm to encourage resin flow and setting.
good luck.... olewill
 
Thank you Mono. As someone who has been involved in composite design and manufacture professionally, I do actually understand something about the subject including the chemistry and it is really annoying to be shouted down by the vociferous idiots on this forum who are merely repeating folklore. I did actually predict that response in my post! It's nice to know there is at least one other person on the forum who knows the subject in more depth. The acetone wipe is a very good point too but I would not "soak" in acetone, as it has a tendancy to break down the cross linking of substrate layers. Apply with a soaked linen rag and stop when the surface starts to feel tacky, then layup the first layer of CSM within 4 hours. When I was building minehunters this was the procedure demanded by Lloyds for any laminate more than 72 hours old. If its good enough for a minehunter it should be good enough on a yacht!
 
Re: Photo and Diagram

Jonjo,
Your photos make everything clear. This is a pretty awful design and will be considerably improved by your proposed mod. I now agree with your idea completely. The cross beams (floors is actually the correct term) are bounded by logitudinal stringers forming a box section grid. Thats actually great. Unfortunately the keel, which should really be attached directly to this superbly rigid structure isn't attached to it at all!!!! The bolts actually go through the thin laminate of the hull within the box and flexural (side to side) loads will tend to cause very high stress in the hull around the bolts. I would not worry about the load on the hull when the boat is ashore though as the vertical load will be transmitted up to the floors. What I would do is clean the whole thing up and not be afraid to be fairly aggressive with a flap wheel. Then as my reply to the other post agreed, give the whole thing a good wash down with acetone (I should have said that in my first post) Remove the nuts from the bolts (assuming you have nice long bolts) and layup using polyester or vinylester resin and CSM for the first two layers and then alternate biaxial cloth and CSM to the maximum thickness you can achieve within reason tucking the whole thing closely into the bolts. When you have finished get some stainless steel washers or plates cut that are about 4 inches square and bed these down on resin soaked CSM over the existing bolts. Remember that the objective is to transmit the load to the floors so carry the new glass up to the top of the floors and stringers with minimal fade out. I repeat that you will find this so much easier to do in polyester and there is, now that I have seen the thing, absolutely no advantage in using epoxy at all. Just keep the whole thing very clean and dry and reasonably ventilated. Also remember that breathing acetone and fumes from polyester is not healthy but epoxy is lethal and can actually kill you. If you don't believe me read the EDS sheets on the products.
 
I didn't answer this point in my other post Jonjo but don't worry about it. The stresses outside of the frame are very low. There is no chance of a stress fracture outside of this area at all.
 
Re: Photo and Diagram

Hi Mike

Is usual (and not regarded as bad) practice on glass keelboats for the keelbolts to go through the plating and not the floors. The plating only has to be sufficient to transfer the stress into the grid and with stiffness sufficient to prevent pumping of the keel going to windward in seas, on which point the 12-13mm plating thickness quoted as existing by Jonjo would not be unusual for a 40 foot boat from what I can determine (but thickness obviously dependant on the length to breadth ratio of the panel between the floors).

Jonjo's comment that the larger Match failures appear to be failure at the floor to panel join fit in with what is shown in his photos as there appears to be no tabbing at the joint but, of course, the designer may have been satisfied there was sufficent fixity through analysis. ABS actually requires a minimum and maximum dimension for the tabbing which from what I can find is 50mm minimum but no more than 9x the thickness of the panel ie no more than around 108mm in Jonjo's case, so on the face of it the fix by adding thickness to all the plating between the floors still would not comply with ABS unless the method was proven by first principles analysis.

I agree that what Jonjo intends doing does not look detrimental on the face of it but given a light hull construction and no understanding of the profile of the designed for hull deformations (and we are looking at a section of the surrounding hull that includes the rigging deformations as well) but I am not a naval architect so it is not something I would undertake myself without very good advice.

Alot of good boats get stuffed up by amateurs (and indeed the designers don't get it right all the time), which kinda gets back to what you asked before - if there is no problem with the boat, or known ones on sister vessels, why do it? Maybe Jonjo has become a little too sensitive to comments from Manky Auwld Boat owners that all Bav's are crap and about to fall apart /forums/images/graemlins/smile.gif - structurally I haven't heard of any evidence of any such issue (outside of the add on bits such as the joinery).

John
 
Re: Photo and Diagram

Actually John, I don't agree with you this time. Having been involved with the design and build of 8 fairly large composite sailing boats and the refit of more, the keelbolts, where there were any, nearly always went through the floors or a heavily reinforced area between them. Mirabella V, which I was involved in, has a lifting keel but the mounting structure is directly onto the framing not the plating.

I do agree that if you attach the bolts through the hull plating it only needs to be sufficient to transfer the load to the floors but with the very high moment on the keel (about 4ft 6-5ft in this case?) and a totally rigid keel which does not flex at all, the thickness required to do this is in the order of 25-30mm minimum over the width shown. Boxing the plating around with a frame will ensure that no flexing takes place outside it which means that the flexural stress is concentrated in a very small area. It is not possible to calculate the compressive and tensional loads without knowing what reinforcement is used, but in this case the structure has to be sufficient to withstand flexural loads which is generally a function of thickness and according to the details given the flexural load on the plating is applied over 4 inch square washer. The ratio of load on the keel end to a 4 inch area means that every tonne of side load will exert a 15 tonne load on the washer. Taken another way, if the keel is 8inches wide at the root where it joins the hull there is a 4 inch moment between the bolt centre and the keel edge meaning that any side load applied on the end of the keel will apply a straight pull of 15 times that value on the bolt.
Looking at my records I can see comparitive test results for flexural and tear strength (a straight pull on a bolt at 90 degrees to the sample) that imply that the suggested thickness of plating would fail at less than this figure making the suggested modification highly desireable and the record of failures more than folklore.
I now understand why, as in this case, good surveyors insist on inspecting the area around the bolts for cracks on these boats. In this case there aren't any indicating that the boat has not been subjected to hard use I suspect. What this guy is doing will therefore be good insurance and make sure that the boat is very much more capable of taking an impact load on the keel which is potentially very high indeed if taken at speed. That is exactly what happened with Mirabella and while it didnt do too much good to the keel and lifting gear the hull structure was undamaged. Proof of the pudding I think!
 
Re: Photo and Diagram

I am only talking about small yachts in the size range of the Bav talked about Mike. Not big ones.

John
 
Re: Photo and Diagram

What's the difference John? The principle is the same surely? Just a different scale of numbers. If he is doing 6 knots and hits a rock this "little ship" will, according to my rough calculations anyway, be in grave danger of having the keel part company with the hull. OK if he never grounds it of course and it is always treated gently when brought ashore, but what about when S**t Happens?
I really don't see what anyone could object to with the mod he proposes and it will raise the factor of safety enormously. Also I have in the past owned 2 monohulls of less than 36ft OAL where the keels were bolted through the floors and still consider this "best practice". Do you not agree?
 
Re: Photo and Diagram

Boatmike. If you are still around, could you explain how a keel bolt can go through a "floor" and still be capable of sealing.

I can not picture the structure that has enough compression strength. Truth be told we have no bolts on ours and have only worked on Ali, wood or steel super yachts.
 
Re: Photo and Diagram

Hi Mike

I think you are reading too much into what I have said. For example, regarding your challenge on keel bolts all I have said is that it is common practice to bolt them through the plating between the floors on similar sized boats. That has been done for many years and I don't think there is any evidence that this is not a satisfactory method and suspect that it may have some good points on lightly built boats. I did not claim it was necessarily the best way but in the end we are not redesigning the boat.

The guts of what I am saying is that it is quite possible there is no problem at all with the proposed mod (but there are some things that I wonder about - such as why do ABS limit the tabbing width?). But that if it were me I would spend 5 minutes sending an email to the original designer and bounce the concept off him ( and after the experience of the bigger Match they have almost certainly relooked at the smaller one). He may very well come back and say, "No problem with the mod", or "No problem with the boat as it is, we have checked", or he may not. He may, for reasons of his association with Bav come back and say "Not telling yer" in which case it would be sensible, in my opinion, to wonder why he said that (looming probs with the boat or just Bav having the wagons in a circle?) - I would then seek the opinion of a very experienced naval architect or yacht designer in the construction. He may just say "No problems" and at worst it has then just cost one 30 minutes of his time. Or he might point out some issues from his knowledge in which case one would be happy to spend more to get the right answer.

All seems common sense to me. After all, if I was managing it for a client I would regard it as good insurance to check it out with the original designer and I could do that in the same time it has taken me to write this post. If a later problem arose with the boat's structure, related to the mod or not, one would be regarded as not having done ones job properly if the owner asked "Did you check out the mods with the original designer?" and one was forced to confess "Well, no I did not" /forums/images/graemlins/frown.gif.

Cripes, in the time it has taken over several posts to reitrate the same points I could have bounced the concept off the original designer and got his blessing or not. And if not I would have have gotten most of the way down the track in getting the opinion or solution from another /forums/images/graemlins/crazy.gif.

Jonjo may wish to spend 5 minutes bouncing the concept off the original designer or he may not. Is his decision but would seem silly to me not to. As I have said, I would not buy a modified light boat without the mod having the written blessing of the designer (or failing him of another designer regarded as competent in similar vessels).

John
 
Re: Photo and Diagram

Yes Neil,
Briefly as I am just waiting for water to get off my mooring!
If the floors are simply "top hat" sections, or foam filled as I suspect these are the short answer is "you cant" because as you rightly say, the compression strength would be insufficient. To bolt through, the section would have to be designed to take the load, usually on small yachts by laying a wooden hardwood former down on crestomer paste or similar resin, and then glassing over it. It also needs a recess built in to sink the bolt head and nut under the surface to allow the decking to be laid on top without the nut sticking through. Unless the boat was designed this way, and as John says, many aren't, the alternative is to bolt through in between the floors. There is nothing inherently wrong with doing this but it requires that the whole area between the floors is reinforced to a sufficient thickness and bonded to the floors themselves. This is not "tabbing" it is creating a complete inner moulding that is a structure in itself and will transfer the load to the floors. Thats fine. All that is wrong here is that this area is in my opinion, and seemingly others too (or the issue would not have been raised in the first place) insufficiently reinforced. Several builders I have been involved with have solved this problem elegantly by making a complete grid moulding, with a gel-coated surface which has the area between the floors laid up to a generous thickness and then bonding the whole thing down into the hull on resin making the thickness where the bolts go through sufficiently thick and creating a nice clean bilge well. There are many ways of killing a cat (apologies to John) but whichever method is adopted it has to be done properly!
 
Re: Photo and Diagram

John,
I think I have covered most of your points in the reply to Neil but your point on tabbing, or boundary angle design, is correct. Normally boundary angles are not required to be more than a certain width (which under DNV and Lloyds rules is relative to the thickness of the substrate materials and not a fixed value) because to do so would create a "Hard spot " in the structure. Stresses at the edges of this area would be raised because it cannot "flex". This area is not a boundary angle though. It is increasing the thickness of the whole area between the floors and longits to a uniform thickness and continuing the same thickness right up to the top of the floors producing a "tray" If this was submitted to ABS, Lloyds, DNV, or God himself it would have approval. Now, the tide is coming in and I can at last get Peregrine away so Live long and prosper and have a nice day folks. Anyone in Yarmouth later, see you there (if there is any room left for me)
 
Re: Photo and Diagram

Thanks boatmike. As I hate wood in fibre glass boats I personally would go for inverse floors. In the post earlier I tried to point out that those German drawings were actually proposing U shaped cross beams where the bolt went through the base of the U. A little cross strength at the top of the U but not obscuring the bolts would be a compromise of both ways.
 
Re: Photo and Diagram

[ QUOTE ]
Jonjo may wish to spend 5 minutes bouncing the concept off the original designer or he may not. Is his decision but would seem silly to me not to. As I have said, I would not buy a modified light boat without the mod having the written blessing of the designer (or failing him of another designer regarded as competent in similar vessels).

[/ QUOTE ]
I will do this, appealing direct to J&J designs is not something I had considered. The Match 35 has now disappeared off the Bavaria web site even though their agents are still linking back to URls that return 404 not found errors.

If production has creased I would be more likely to get a response but I am still not hopeful. My Bavaria agent was willing to discuss implementing the mod for a £4,000 fee which seemed a lot for grinding back and then laminating 3 trays measuring 100cm x 25cm x 20 high with the keel left insitu.

The surveyor who looked at the hull while weight was loaded on the keel and then reviewed the internal bilge reinforcement commented that it all looks very substantial and said go forth and enjoy sailing your boat. Then he added "but if you did want to increase reserve strength" laminate in another 5mm plus fit a second backing plate to the front 4 keel bolts similar to the central one.
 
Re: Photo and Diagram

[ QUOTE ]
I do agree that if you attach the bolts through the hull plating it only needs to be sufficient to transfer the load to the floors but with the very high moment on the keel (about 4ft 6-5ft in this case?)

[/ QUOTE ]
The keel alone is about 5' 10' deep and with the hull daft included total draft is 7' 2". The keel has a simple dagger board shape with slight flaring at the bottom but no bulb. I guess the COG is no more than 60% of the keel length down from the hull. At the hull the keel root is 3 feet long and 1ft wide (max).

[ QUOTE ]
if the keel is 8inches wide at the root where it joins the hull there is a 4 inch moment between the bolt centre and the keel edge meaning that any side load applied on the end of the keel will apply a straight pull of 15 times that value on the bolt.

[/ QUOTE ]
I have found my original detailed measurements taken from the bilge. Of the 11 keel bolts 6 will deal with most lateral loads when the boat is heeled. The 3 windward bolts would have an average distance of 25cm from the leeward keel edge under compression. The enlarged steel backing plates I have in mind add another 15cm to this leverage distance.
 
Re: Measurement update

[ QUOTE ]
implementing the mod for a £4,000 fee which seemed a lot for grinding back and then laminating 3 trays measuring 100cm x 25cm x 20 high with the keel left insitu.

[/ QUOTE ]
Now found my origial notes, the 2 largest trays would be 85cm x 29cm x 20cm.
 
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