tape joints outside vs inside vs rebated etc

[fallguy1000]

Okay, so the other day a reputable builder told me when you do a 2-4-6-8" outside tape joint over relief joints; you tape the 8 first, then the 6 then the 4, then the 2. He said the rationale is that if you sand through the 4" a little and the 6" a little and the 8" a little in fairing you still have most of an 8" joint holding the boat together. What I don't get is why then are you bothering to build up the join with the other two?

I really thought the purpose of staggering the joints was to get incrementally more grab onto the thing you are trying to hold, so if the 8" tape lets go, the 6" tape is still working, etc.

Has anyone heard of anytime you would tape in order of largest to smallest as he suggests?

Isn't this in the tutorials here somewhere, too?

thanks

[Evan_Gatehouse]

The staggered tape width is to gradually decrease the strength and stiffness of the joint so you don't have a stress concentration/hard stop.

If you are patching a hole, aeronautical composite practice is "biggest piece of cloth first". Typically marine practice is "smallest first".

But I don't have a strong rationale for a chine joint. Usually I would do biggest / widest last. That is more typical in boat construction.

[dbcrx]

I've been asked this a few times. I always go bigger to smaller. That's how West Systems described it in their guides and I'm not sure I've read anywhere that it should be the other way round.

My theory is that if you do the smaller layer first then each layer only bonds a small amount onto the original surface, and you can get small air pockets around the edge of each layer. This hopefully shows what I mean:

Untitled.jpg (41.65 KiB) Viewed 933 times

I'm no structural engineer, but I'm fairly sure I could guess which method would be stronger.

[TomW1]

Fallguy I agree with the others you always start with the largest first and go to the smallest. This allows you to have a strong beam type structure as well as feather the edges of each piece for fairing.

Tom

[fallguy1000]

Unless I'm wrong Evan is telling me to go smallest to largest. Usually "I would do biggest / widest last"

The designer specified the joints 6-6-8 on the inside panel joins, and he specified double glass on the bottom. I laminated only a single skin on the bottom on the inside and the outside in order to wrap the second skin over the panel joins (especially since there is a vee midships.

In order to hold the panels in place, I had to screw the panels in with panel washers and I elected to screw them through the rebates, so I put in 4" panel joins in between the panel washers, and I was planning to remove the panel washers and fill in the balance and exceed the spec by going 4 6 6 AND run the second panel lamination all the way up and onto the side to 50mm above the WL and consider that the 8" join.

Does that sound decent? I hate to bother RW with all the build stuff all the time.

There are no rebates on the inside of the boat, but putting the screws into the panel rebates will be easier to repair since those areas are getting taped on the outside.

Thanks for any replies.

[BB Sig]

I would hope RW would be glad to answer your questions on your build. Jacques had been great answering questions. The designer would have the best input on how to build his design if you follow his methods.

[fallguy1000]

I got RW's blessing on tabbing the panels in and then laminating the bottom piece. I am making a fillet with 50/50 balloons n cabosil. I don't like cotton in fillets.

I think it'll end up being tabbed in with 4" and then finishing the tabbing after removing the washers, then I will run two 6" tapes each side and then laminate the bottom join up to the WL. I am going to run the fabric with the 0 strands on the transverse.

Thanks for the replies. RW said the wider tapes first is used for fairing situations.

[Jaysen]

Did RW comment on the use of balloons? I only ask because of a few previous suggestions that they should not be used for structural work. The balloons aren't typically very strong.

[dbcrx]

Did RW comment on the use of balloons? I only ask because of a few previous suggestions that they should not be used for structural work. The balloons aren't typically very strong.

What he said.

[narfi]

Did RW comment on the use of balloons? I only ask because of a few previous suggestions that they should not be used for structural work. The balloons aren't typically very strong.

I think you want similar type to similar type for your fillets, for plywood you want an epoxy/wood flour fillet, for foam you want an epoxy/balloons mix? (not sure if I am right or wrong, but thought I had read that somewhere.....)