Bulkhead repair suggestions Gemini 105M

[s/v Jedi]

Originally Posted by smj

A well done scarf glued in with epoxy would probably be fine without the glass, reaching the same strength as original. Or a butt joint like you said but could grind out a taper on the joint and glass tab the taper would also work fine.
I see no reason for a huge part of the bulkhead to be removed as someone stated earlier for such a small piece of rotten wood, but everyone must repair in the manner in which they feel comfortable?

Indeed. I have seen many larger repairs but they all had damage indicating that the original construction was too weak. I remember a good video from the Young Barnacles who also upgraded to carbon fiber chainplates.

[coopec43]

Originally Posted by tharch

Coopec43

Thanks fir the link. I read through that. When considering similar areas of repair, they seem to be doing the save thing, cut out rotten part, put a new piece on and fiberglass it. Main difference appears to be that the glassing extends to the hull. Am I missing something?

Gemini bulkheads don't seem to have been designed that way. They appear to be designed with some give. I don't know enough about boat structures to alter a fundamental design criterion.

Thoughts?

I would extend the fiberglass to the hull. I would ensure the bulkhead is "tabbed" heavily to the hull all way around.

But a word of WARNING! I am not familiar with lightweight multi-hull construction so what I think may not be correct.

You might be interested in this? (Is yours a M105Mc?)

https://chesapeakemultihulls.org/wp-content/uploads/2020/11/Gemini_Owners_Manual_105Mc-1.pdf

[tharch]

Originally Posted by coopec43

I would extend the fiberglass to the hull. I would ensure the bulkhead is "tabbed" heavily to the hull all way around.

But a word of WARNING! I am not familiar with lightweight multi-hull construction so what I think may not be correct.

You might be interested in this? (Is yours a M105Mc?)

https://chesapeakemultihulls.org/wp-content/uploads/2020/11/Gemini_Owners_Manual_105Mc-1.pdf

I will check that link. It is a 105M

Not the MC
Looks like gemini by design has bulkheads that have some give, to reduce the load on the light weight hulls
Thanks

[tharch]

Originally Posted by s/v Jedi

Indeed. I have seen many larger repairs but they all had damage indicating that the original construction was too weak. I remember a good video from the Young Barnacles who also upgraded to carbon fiber chainplates.

Thanks Jedi
I saw his videos too about the chainplates. Fascinating mix of old and new

[tharch]

Originally Posted by smj

A well done scarf glued in with epoxy would probably be fine without the glass, reaching the same strength as original. Or a butt joint like you said but could grind out a taper on the joint and glass tab the taper would also work fine.
I see no reason for a huge part of the bulkhead to be removed as someone stated earlier for such a small piece of rotten wood, but everyone must repair in the manner in which they feel comfortable?

Thanks smj. I am all for making less work for me too
It is in a fairly accessible place on both sides. I am thinking of a butt joint, then grind and glass and a doubler plate on the back for some assurance.

[coopec43]

Originally Posted by tharch

I will check that link. It is a 105M

Not the MC
Looks like gemini by design has bulkheads that have some give, to reduce the load on the light weight hulls
Thanks

What about this one then?

https://www.yumpu.com/xx/document/vi...manual-gemcats

[gulfislandfred]

Forget about hiding the repair. It's hard to do, and make you look dishonest. A strong repair shows best practice.

Cut out the rotten plywood. Put in a new filler piece to fill that space.
Then put a new piece of plywood (or aluminum plate or really thick glass panel) with an eight to 12 inch overlap, bigger than your filler piece, glued and through bolted to the bulkhead, on the other side from the chain plate, and bolt the chain plate back on, with longer bolts.
If you want to make it look good on the chain plate side, put one or two layers od glass cloth in epoxy over the repair, and paint it, or just paint it.


If the bulkhead to hull joint has not shown any problems, leave it alone!

[coopec43]

[QUOTE=gulfislandfred;3902258]Forget about hiding the repair. It's hard to do, and make you look dishonest. A strong repair shows best practice.

Cut out the rotten plywood. Put in a new filler piece to fill that space.
Then put a new piece of plywood (or aluminum plate or really thick glass panel) with an eight to 12 inch overlap, bigger than your filler piece, glued and through bolted to the bulkhead, on the other side from the chain plate, and bolt the chain plate back on, with longer bolts.
If you want to make it look good on the chain plate side, put one or two layers od glass cloth in epoxy over the repair, and paint it, or just paint it.


If the bulkhead to hull joint has not shown any problems, leave it alone![/QUOTE]


That is the part that worries me but some on this thread are saying it doesn't have to be joined to the hull!


This is Post #3

tharch
Registered User


Join Date: Feb 2024
Posts: 58


Re: Bulkhead repair suggestions Gemini 105M
Hi coopec43
It is apparently cherry laminate and it does not appear to be glassed to the hull. It seems to insert in to a slot created by a fiberglass lip

What is the point of repairing the bulkhead if it isn't attached to the hull?. (Probably 100kg 20ft(?) up the mast (in a choppy sea) swing to-and-fro)

I think tharch needs expert advice and not advice from people on a forum thread.

[gulfislandfred]

If the boat has been in service for a while, and others of the same design have not failed catastrophically, I would trust the designers, and leave the bulkhead as built.


Not a bad idea to research the issue, see what other owners have done, and decide if action is indicated. If action is indicated, then do ALL the bulkhead to hull joints.

[smj]

[QUOTE=coopec43;3902444]

Originally Posted by gulfislandfred

Forget about hiding the repair. It's hard to do, and make you look dishonest. A strong repair shows best practice.

Cut out the rotten plywood. Put in a new filler piece to fill that space.
Then put a new piece of plywood (or aluminum plate or really thick glass panel) with an eight to 12 inch overlap, bigger than your filler piece, glued and through bolted to the bulkhead, on the other side from the chain plate, and bolt the chain plate back on, with longer bolts.
If you want to make it look good on the chain plate side, put one or two layers od glass cloth in epoxy over the repair, and paint it, or just paint it.


If the bulkhead to hull joint has not shown any problems, leave it alone![/QUOTE]


That is the part that worries me but some on this thread are saying it doesn't have to be joined to the hull!


This is Post #3

tharch
Registered User


Join Date: Feb 2024
Posts: 58


Re: Bulkhead repair suggestions Gemini 105M
Hi coopec43
It is apparently cherry laminate and it does not appear to be glassed to the hull. It seems to insert in to a slot created by a fiberglass lip

What is the point of repairing the bulkhead if it isn't attached to the hull?. (Probably 100kg 20ft(?) up the mast (in a choppy sea) swing to-and-fro)

I think tharch needs expert advice and not advice from people on a forum thread.

I think the bulkhead maybe tabbed into the hull but that part isn’t compromised. The bulkhead to deck section maybe compromised but that appears to be what is called a floating bulkhead, in no way physically attached to the deck but floating between two fiberglass lips.

[coopec43]

Mmmmn I don't like it. A mast stay attached to a floating bulkhead?


https://www.spinsheet.com/boat-revie...ed-boat-review

[s/v Jedi]

Originally Posted by coopec43

Mmmmn I don't like it. A mast stay attached to a floating bulkhead?

https://www.spinsheet.com/boat-revie...ed-boat-review

But physics don’t care for our opinions. Engineers have determined it works and reality has supported that. Apparently it is how airplanes are built too.

I see many bulkheads that have foam between the bulkhead and the deck, then a thin layer of glass over that foam, which is contoured like fillets, to keep it in place. This isn’t a structural connection but rather the same function as the channels of this Gemini.

They avoid print-through this way.

[coopec43]

Originally Posted by s/v Jedi

But physics don’t care for our opinions. Engineers have determined it works and reality has supported that. Apparently it is how airplanes are built too.

I see many bulkheads that have foam between the bulkhead and the deck, then a thin layer of glass over that foam, which is contoured like fillets, to keep it in place. This isn’t a structural connection but rather the same function as the channels of this Gemini.

They avoid print-through this way.

You haven't convinced me (I think "ll give catamarans a miss)

What are bulkheads in aircraft?






A bulkhead is a physical partition that divides a plane into different classes or sections. Typically, a bulkhead is a wall but can also be a curtain or screen. Bulkheads can be found throughout the plane, separating the seats from the galley and lavatory areas.