[marcjsmith]

@Skipper Jer instead of visqueen. packing tape. its works really good at not sticking to cured epoxy. if the wood is receptive I would tape a couple overlapping layers to your wooden form and then as a bonus wax it. 99% you've got no chance of anything that squeezes past the peel ply sticking to the wood.

 

[pdqaltair]

Jeff I like your suggestions. I made templates that fit tightly over the original surfaces to insure I don't exceed the dimensions that fit inside the trunk. The travel lift isn't free. I do have some plywood that can be used to squish the glass flat. Instead of wax paper I plan on using visqueen plastic sheeting. I need to make some deep reaching clamps.

I would suggest against carbon for this.

• Carbon is so stiff the carbon will actually take ALL of the load. The 1708 will barely contribute, other than holding the carbon in place.
• Fiberglass is very nearly as strong per volume. Not as stiff, but as strong. And the stiffness will match the 1708, so they all work together.
• Fiberglass is much tougher (impact resistant) than carbon. Similar strength, but bends farther without breaking.

Carbon could save a fraction of an ounce. Down low, who cares.

I only use carbon where I have to match the stiffness of other carbon parts. Otherwise, glass goes with glass.

 

[Jeff_H]

I would suggest against carbon for this.

• Carbon is so stiff the carbon will actually take ALL of the load. The 1708 will barely contribute, other than holding the carbon in place.
• Fiberglass is very nearly as strong per volume. Not as stiff, but as strong. And the stiffness will match the 1708, so they all work together.
• Fiberglass is much tougher (impact resistant) than carbon. Similar strength, but bends farther without breaking.

Carbon could save a fraction of an ounce. Down low, who cares.

I only use carbon where I have to match the stiffness of other carbon parts. Otherwise, glass goes with glass.

Good points, I threw in the idea of adding carbon because I would be concerned that there may be fatigue due to flexure in the remaining existing laminate. The idea behind adding the carbon was to limit flexure rather than add strength.

Jeff

 

[pdqaltair]

Good points, I threw in the idea of adding carbon because I would be concerned that there may be fatigue due to flexure in the remaining existing laminate. The idea behind adding the carbon was to limit flexure rather than add strength.

Jeff

I get that. But carbon greatly increases the stress between the layers and can hasten delamination unless the ends are tapered/blended very carefully.

I have had bad experiences, when I used it just to make something stiffer, and good experiences, when I used it as a part of a designed carbon structure. When in doubt, I always stick with what was there before.

 

[Michael Bailey]

I broke my boat. There is a shaft attached to the keel that cracked. The shaft helps to stabilize the keel when the keel is deployed. The assembly is out of the boat and partially repaired. The last step is to apply 6 layers of bi-axial cloth with
epoxy. I was planning to spray adhesive on the non-saturated cloth to hold the cloth in place until the epoxy cures. The red area is the original surface is not in the repaired area. Still considering vacuuming bagging the entire repaired area. Crude diagram below. Comments and recommendations sought. View attachment 157788

How would you determine the fix is strong enough without doing it and trying to sail it tilo failure?

 

[pdqaltair]

How would you determine the fix is strong enough without doing it and trying to sail it tilo failure?

Always difficult, but not impossible.

• When you grind away the damage you will find out how much glass was used initially, and how much was core. Use several layers more.
• Bevel far enough (at least 12:1 so that the bond is stronger than the glass.
• Use stronger materials. For example, I'm guessing this was laid up with mat and something like 1708. Use less mat and add some uni, which has a lot more strength in the required direction.

But it is very hard to know until you get into it and see how it was built.

There is also the question of how it broke. Was it wear and tear or did someone hit a rock?

 

[Skipper Jer]

There is also the question of how it broke. Was it wear and tear or did someone hit a rock?

There is no visible damage (dents)
to the bulb that a rock hit would leave. The keel shaft is also used to support a gin pole. The crack was discovered as the mast was raised after getting the anchor light and wind instruments to function. We are the third owners of this boat. I don't know if the previous owners ever used the gin pole. Once the keel assembly was removed it became obvious why it cracked. As they say a picture is worth a thousand words. A hole was drilled in a wrong place. It was filled with"stuff" gel coated over then another hole was drilled a few inches above. Also there various voids thru-out the structure, one is 2.5 inches deep. These voids have been filled with a mixture of chopped fiberglass strands and cabosil filler.

 

[Jeff_H]

There is no visible damage (dents)
to the bulb that a rock hit would leave. The keel shaft is also used to support a gin pole. The crack was discovered as the mast was raised after getting the anchor light and wind instruments to function. We are the third owners of this boat. I don't know if the previous owners ever used the gin pole. Once the keel assembly was removed it became obvious why it cracked. As they say a picture is worth a thousand words. A hole was drilled in a wrong place. It was filled with"stuff" gel coated over then another hole was drilled a few inches above. Also there various voids thru-out the structure, one is 2.5 inches deep. These voids have been filled with a mixture of chopped fiberglass strands and cabosil filler.



View attachment 157799

I am glad that you put up the picture because as much as I hate to say this, that is not an easy repair. The repair is basically reengineering a highly stressed component that was not properly engineered and/or constructed properly in the first place.

To explain, there appears to be significant stress cracks on a wide area of the struct portion of the keel and reaching all the way to the foil portion of the keel. That strut has to resist lateral, torsional and fore and aft loadings. There is no room for error. The more serious part of what is happening is that the strut seems to be splitting apart fore and aft as well as horizontally, and there multiple horizontal cracks that extend through the strut above and well below the worst set of cracks at the bolt holes. This is not an easy repair, and may not be one that someone takes on as one of their first projects.

The new laminate will need to wrap around around the entire struct since the strut is splitting apart on its center seam as well as failing in bending in both directions. where the strut radiuses out to meet the foil. and below the big vertical split.

Frankly I would contact the manufacturer and see whether they can give you assistance. Minimally they should be able to give you a laminate schedule for the strut. They may be able to tell you whether other's have had the problem and how it was handled. More seriously, they may be willing to give assistance in getting a new replacement keel at some kind of reasonable price.

But looking at that, there is no reliable way to make that repair with the keel standing on end.

Jeff

 

[Skipper Jer]

Minimally they should be able to give you a laminate schedule for the strut. They may be able to tell you whether other's have had the problem and how it was handled. More seriously, they may be willing to give assistance in getting a new replacement keel at some kind of reasonable price.

Others have had failures. There is a 26 foot version that have had several bulb separations. There is a 32 that broke the strut off by hitting it on a garage while backing in. Yes owner's fault. The builder offers an "upgrade" that instead of using fiberglass and resin for the strut, it uses a 2x2 inch stainless steel tube for about 9 grand. The upgrade includes a different shaped bulb. I have contacted the builder a few times with little success. My thought is since the boat is a 2001 and has sailed successfully for many years with the way the strut was built, it will sail for many more years with the area reinforced. After removing the gel coat I inspected the core very closely for additional cracks and found none. I have removed at approximate .2 inches of the core in all areas. That will provide room for several layers of 1705 (17 oz bi-axial no matt) and a few layers of uni (S glass 6 0z). As far as forces, the strut never takes the full weigh of the bulb since the assemble is hung from cables. Also I think some of the other forces you mention (lateral, torsional and fore and aft loading) are transferred to the hull of the boat due to the tight fit. So I asked Chatgpt to calculate the laminate schedule of the uni and bi axial glass using epoxy resin. This is what it came up with:

Thickness

~2.5–2.7 mm .1 inches

Tensile Strength 280 MPa 40610.6 psi

~c

Flexural Strength ~900 MPa 130534 psi

Tensile Modulus ~26 GPa 3.771e+6 psi

My input to Chatgpt: calculate the strength of the following laminate schedule. 3 layers of 1705 biaxial 17 oz cloth interleaved with 3 layers of 6 oz of s glass cloth using epoxy resin. Of course it all depends of how well the new glass adheres to the present structure, how well the cloth is wetted, no air bubbles in the laminate, and no contamination. The total amount of old structure removed is .4 inches (.2 on each side). I'm going to remove some more gelcoat in the vertical direction.

 

[Skipper Jer]

And I asked chatgpt to calculate the strength of a 3x5 hollow tube. My input: calculate the strength of the a hollow square tube that is 3 inches by 5 inches with thee walls built from the following laminate schedule. 3 layers of 1705 biaxial 17 oz cloth interleaved with 3 layers of 6 oz of s glass cloth using epoxy resin.

The results:

Wall thickness

0.135 inches

Moment of Inertia (I)

3.26 in⁴

Estimated Flexural Strength

~60,000 psi

Max Bending Moment

~130,400 in-lb (~10,867 ft-lb)

 

[pdqaltair]

Assuming Chat is correct (not interested in checking the calcs), the bending moment of the bulb with the boat laid over is potentially about 6' x 2200 = 13200 ft-pounds (you didn't give me the exact numbers) without dynamic loading. You really need a 3:1 safety factor even for this worst case, given the uncertainties. I don't know where the peak bending force is; it looks like ti could be much lower ... and then there is the matter of the crack lower down. Normal sailing loads are a complex mix of lateral force, lift, bulb bending moment, and dynamic forces, but many times less, which is why it has not just snapped off.

Just not enough information. It the very least, just make it 50% stronger than it was before. No certainty without a lot more information.

 

[colemj]

Seaward was bought by Island Packet, and they no longer build/sell them. Nick Hake has his own company now, so maybe try contacting him there? NH Designs - NH Designs

I looked up some pictures of your boat model, and can't figure out what that hole is even for. All the pictures show the keel raised or partly down, with that hole just sitting there in the strut. Do you stick a dowel in it if you need to release the tension from the uphaul line? If so, I don't see how it made a difference on the first hole such that they needed to redrill it.

Now that I understand better what this is (always use a picture as a lede!), I agree that it isn't a straightforward repair like I originally thought. It is somewhat similar to repairing a daggerboard on a catamaran, although you have that weighted bulb to account for. So in this case, it is going to be more of a rebuild than a repair. Still possible to do without extensive expertise, but you are going to remove a lot more of the existing laminate, possibly repair some coring, and rebuilding the laminate with structural paths in mind. I'd at least fill in that mistake hole with core or thickened resin.

I don't think there is an issue working on this vertically, other than the obvious issues that one has to be able to reach it and it needs to be fixed in place enough to grind on, etc. I assume you will have some scaffolding and chocks or something for this. I do now think you will need to wrap the laminate and not just do individual sides, but the picture shows this will be no problem.

If it were me, I'd be using 23oz triaxial for this. That will incorporate your uni (orient it correctly), handle the rounded corners well enough to wrap, require fewer laminate layers, and get rid of the CSM. The CSM on 1708 biax does nothing for you here but bulk the laminate with no added strength. BTW, I'm assuming you mean 1708 and not 1705? I've never seen 1705, but it could exist.

Mark

Edit: I overlooked that you have already ground this back and see no core damage needing to be repaired. That's good. Fill that mistake hole.

 

[colemj]

Check out this video starting at 4:40.

I understand this keel a lot better now. There is no significant torsional moment on the thinner part. It is all lateral moment with a small amount of fore-aft, and it is well supported on its span by the trunk, although I suspect in reality the load is born only by the areas at the top and bottom of the trunk. Probably where those wear marks are. This is very similar to a catamaran daggerboard.

I think the worry about structural integrity and loads is less than we have been assuming. It might help to see a larger scale picture showing more of the transition area of the blade to the stick. That bit between the actual foil and the stick part is very important, so I'd make sure that was structurally sound. Your challenge there will be making sure to keep the tight tolerance to fit the trunk very well in this area.

Mark

 

[Skipper Jer]

and can't figure out what that hole is even for

The holes, there are 3, serve two purposes. A stainless steel tube is inserted, then tension on the winch can be released. The holes are also used to hold the gin pole when raising or lowering the mast. The winch is attached via cable to the foil, not the shaft. There is no lifting on the shaft.

I'd at least fill in that mistake hole with core or thickened resin.

I did fill in the mistake hole with 1/2 inch chopped strands and thickened resin.

I'm assuming you mean 1708 and not 1705? I've never seen 1705, but it could exist.

The place I ordered the 1705 described it without the matt.

 

[colemj]

The holes, there are 3, serve two purposes. A stainless steel tube is inserted, then tension on the winch can be released. The holes are also used to hold the gin pole when raising or lowering the mast. The winch is attached via cable to the foil, not the shaft. There is no lifting on the shaft.

I see. Strange that an inch or two made any difference to those functions. Unless that mistake hole wasn't above the deck surface when up all the way.

The place I ordered the 1705 described it without the matt.

Great. You don't want the mat. I've always seen it as 170 or 180, not 1705/1805.

Mark

 

[pdqaltair]

Actually, the very thin the mat serves a very definite reason, improving bonding to vinyl ester and polyester in secondary bonding applications such as this. It is also used when bonding to wood or core, because the wood and core can drain resin away from the laminate. That is what it is made for. Also as the first layer to an irregular surface. It is NOT something that is put on there to save money and it is a very thin mat, so it does not waste much space. For example, uni applied to an irregular surface and also straight to polyester does not bond very well. It's not going to matter what you lay up if your laminate does not form a really good secondary bond to the old polyester.

Apply the 1708 mat side down, to the existing laminate. I would use 1708 on the first layer, particularly in the areas with lots of curves. Then I would switch to no-mat and unit in alternating layers. 1708 can also be used mat-up on the last layer to make fairing easier and to reduce sanding damage to the long fibers of the woven part. You don't want to be sanding the woven part, and you will need a very fair surface to get smooth sliding.

Don't forget that biax is stronger in the primary direction of the fibers than the other way. Pretty obvious. like most sailcloth, it is not a balanced weave.

Not so simple as it seems. Yes, you actually do want this small amount of mat on the first layer. Or just Google the reason. But it probably won't matter either way if your surface prep (very coarse sand) is good and the tapers are long. No worries!

 

[colemj]

I understand the reasons for using a thin layer of mat on the first layer, but there are also other options to reach that goal than mat, and any core should be well-wet out before lamination, so it should not drain resin from the laminate (which it would also do with mat). After that initial layer, mat adds nothing to the layup beyond bulk, and there is no reason for it.

It sounds like the fabric has already been bought, and the repair somewhat underway.

If he wants to buy more fabric, 23oz triaxial would be better, easier to apply, and have less potential for error than alternating layers of 1700 and uni.

I agree for finishing ease that the repair should be left just a tiny amount below the final surface and a layer of CSM applied to bring it level before any sanding and fairing. But even if the biax/uni went above the surface and was sanded down even, thus breaking the long fibers on the outer layer, this is inconsequential WRT strength because it was extra fiber applied than designed anyway.

Mark