Tabernacle / bulkhead failures & fixes . .

Welcome to PocketShip.net! This bulletin board is for builders of the Chesapeake Light Craft-John C. Harris "PocketShip" design, a 15-foot micro cruiser sailboat built from a kit or plans.

For more information on PocketShip, click here: http://www.clcboats.com/pocketship

This site gathers PocketShip builders in one place. Here you can share photos, tips, questions, and---eventually---your sailing adventures in PocketShip! CLC will also post design updates and tips here as they come up.

We'll try to knock down spam as quickly as possible.

Moderator: John C. Harris

Forum rules
Spam or commercial posts will be deleted.
This is a civil forum: no flames or drunken tirades.
Please stay on-topic.
PocketShip's Web Page: http://www.clcboats.com/pocketship
If you need CLC customer service: http://www.clcboats.com/forms/contact_us.html
We'll try to delete spam as soon as it appears.

Re: Tabernacle / bulkhead failures & fixes . .

Postby Bflat on Tue Apr 21, 2015 9:26 pm

...
Last edited by Bflat on Tue Apr 21, 2015 9:36 pm, edited 2 times in total.
Bflat
 
Posts: 206
Joined: Sat Dec 03, 2011 12:15 am

Re: Tabernacle / bulkhead failures & fixes . .

Postby Bflat on Tue Apr 21, 2015 9:29 pm

John in CC wrote:2. A more radical idea (kind of a thought experiment): After raising the mast, insert a pin near the base of the mast/tabernacle and remove the pivot pin. This would relieve much of the leverage on the tabernacle when sailing while still providing the convenience of a tabernacle. You would never sail with both pins in. Reverse the process to lower the mast. A caveat is that the rake couldn't be changed without drilling a another hole in the base, but even this could be alleviated by simply finding the proper rake before committing to drilling the hole for the base pin.


Problem I see is if the halyard fails while sailing upwind, the mast will not fall harmlessly onto the boom gallows. It could and the manual says, "tear the tabernacle right off the boat in a cloud of splitters"...


Oh yeah; I forgot about that. "Nix" that idea.
That still leaves my thoughts 1 and 3 in my previous post (mast rake and/or moving the chainplates aft an inch or two). I'm still wondering about those.
Bflat
 
Posts: 206
Joined: Sat Dec 03, 2011 12:15 am

Re: Tabernacle / bulkhead failures & fixes . .

Postby DanaDCole on Wed Apr 22, 2015 7:02 am

Over the years I've discovered that John H. is almost always right. Amazing, isn't it? :D I'd say leave everything "as is" with the recommended rake and always do due diligence before sailing.
DanaDCole
 
Posts: 496
Joined: Wed Sep 25, 2013 2:06 pm
Location: Stillwater, Oklahoma

Re: Tabernacle / bulkhead failures & fixes . .

Postby Bflat on Mon Sep 28, 2015 10:42 am

I made a tapered laminated deck beam and 3/4" backing plate. The bigger beam adds weight and is not exactly endorsed, but might bring me peace of mind.
Attachments
P1050526.jpg
deck beam and backing plate in place. The carlins inset into the beam by only a 1/4" so they do not weaken the beam much.
P1050526.jpg (79.77 KiB) Viewed 2166 times
P1050448.jpg
laminated hardwood deck beam. Tapered ends for looks and to save a little weight.
P1050448.jpg (55.6 KiB) Viewed 2144 times
Last edited by Bflat on Mon Oct 05, 2015 7:43 am, edited 1 time in total.
Bflat
 
Posts: 206
Joined: Sat Dec 03, 2011 12:15 am

Re: Tabernacle / bulkhead failures & fixes . .

Postby Bflat on Tue Sep 29, 2015 4:38 pm

P1050565.jpg
P1050565.jpg (95.42 KiB) Viewed 2103 times
Here's what I did at the bulkhead/cabin top joint. I wetted out a layer of Kevlar followed by a layer of glass followed by a layer of unidirectional carbon tape followed by another couple layers of glass. I don't suppose it will stand up to a major levering motion of the mast due to loose shrouds etc, but maybe it can stand up to a modest mast bending event. At least it can't hurt, I hope.

The above photo was taken after I wetted out the Kevlar, glass, then carbon. I followed that with more glass.
Bflat
 
Posts: 206
Joined: Sat Dec 03, 2011 12:15 am

Re: Tabernacle / bulkhead failures & fixes . .

Postby mark48 on Mon Jul 29, 2019 5:16 pm

Puffin Tabernacle Crack (small size).jpg
Puffin Tabernacle Crack (small size).jpg (65.28 KiB) Viewed 258 times
Greetings,

My tabernacle suffered a crack on the aft portion of the starboard upper side, extending about 9” down from the top. See photo above.

I believe this happened yesterday as the mast was nearly completely raised while on a mooring; we heard a sound (which in retrospect must have been the event) but we didn’t see any evident damage so we sailed anyway (in some pretty gusty wind and had a grand time). We do not recall that the mast was torqued in any significant way during the raising but something must have done this. It’s possible the crack widened during that sail yesterday because the crack was evident today when we prepared to sail again (in lighter air with some gusts and again had a grand time).

I’ve searched the forum for similar tabernacle failures but don’t find any. The most common tabernacle "failures" on the PS Forum seem to be pulling the tabernacle off the forward bulkhead due to inadequate shroud tension.

I know one builder had a tabernacle injury while trailering the boat with the mast up, but has anyone seen or experienced a failure like this?

I welcome thoughts on what I did to cause this and how to avoid it in the future. I also welcome suggestions on repairs. Luckily my tabernacle is removable. It is constructed from 1" cypress (both sides and aft face).

Thanks for your thoughts,

Mark
mark48
 
Posts: 123
Joined: Fri Jun 28, 2013 9:55 pm

Re: Tabernacle / bulkhead failures & fixes . .

Postby Pascal on Mon Jul 29, 2019 5:56 pm

This looks like a wood crack nothing to do with anything you did.
When I build mine I use hard maple glued on 8 mm marine plywood. It has been few years no crack yet... I would not worry about it if I were you...repair may be after sailing season ?
My issue is actually the tiller...wish I made it out of 1 " thickness. it shows a structure crack after my 22 mph day.
Pascal
 
Posts: 97
Joined: Fri Feb 20, 2009 8:39 am

Re: Tabernacle / bulkhead failures & fixes . .

Postby tattoo on Mon Jul 29, 2019 6:47 pm

If you heard a noise while rotating the mast up (or down) while on the water -- it was probably caused by that split on the tabernacl. I think it should be repaired right away so that water won't invade (and weaken) the wood structure. You could drill a 1/4" hole at the end of the crack [a "stop-gap" measure] and several other holes along the crack into which thickened epoxy should be injected. Effort should be made to widen the split (between the holes) so neat epoxy could be forced into the crack. Then sand both sides down to bare wood and apply strips of 10 oz FG imbedded with neat epoxy. If this would result in narrowing the space between the cheeks to where the mast would not rotate freely, then sand further into the wood on the insides of the surfaces of the tabernacle. When finished it should be good-as-new.

BTY, be extra careful when raising any mast while on the water. My neighbor friend was injured when an unseen & silent "wake" rocked his boat while raising his mast. It also severely damaged his expensive aluminum mast and the hinge. The fit of mast to tabernacle (or hinge) is fairly close-fitting -- and even a little hull-rotation can create very large torque forces at the hinge point of a long mast.
Pete McCrary, launched Tattoo Oct '10.
tattoo
 
Posts: 116
Joined: Wed Sep 16, 2009 7:09 pm
Location: Manassas, Virginia, USA

Re: Tabernacle / bulkhead failures & fixes . .

Postby tattoo on Mon Jul 29, 2019 7:56 pm

Upon reviewing the entire thread that I started -- I believe that Tattoo's two failures was not caused by shrouds not being tight enough. They were tight enough, and the chain plates were properly placed. However the mast was fabricated out of southern white pine -- and it was quite light and very flexible. The shrouds did keep the mast (at the mast hounds) from moving forward. And if the mast were stiff enough, then the tabernacle (and bulkhead) wouldn't be pulled forward -- and thus, no failure. But the fore-to-aft-to-hounds triangles were narrow with the peak near "top-dead-center" which (in a strong wind) created tremendous downward compression on the mast -- causing it to "bow" outward in the forward direction. This caused a forward thrust on the mast bolt -- pulling the (top of) the tabernacle away from the bulkhead. For a sufficiently "stiff" mast -- the failure on Tattoo wouldn't have happened. Note: by this analysis the heel of the mast was thrusting against the lower part of the bulkhead -- perhaps tending to self-limit the damage.

I believe that I experienced the same kind of failure on my DN iceboat which has a forestay with shrouds slightly aft of the mast hound and when attached to the ends of the flexable runner plank -- the triangle: deck (at [mast heel] to shrouds [at runner plank] to mast hound is also narrow. In a very strong wind gust (~ 18 > 24 mph) with iceboat at about 50 mph the mast (made of Sitka spruce) bowed to leward and forward very severely (I was sure it would snap) -- to the point that it was damaged beyond repair with a permanent "kink" and general bend. There were many compression ridges on the inside curve of the mast. I think the bending of Tattoo's mast was caused by the same phenomenon -- with the mast bowing forward, the top of the bulkhead couldn't resist.
Pete McCrary, launched Tattoo Oct '10.
tattoo
 
Posts: 116
Joined: Wed Sep 16, 2009 7:09 pm
Location: Manassas, Virginia, USA

Re: Tabernacle / bulkhead failures & fixes . .

Postby John C. Harris on Tue Jul 30, 2019 3:12 pm

Very early on, PocketShip #1 had a crack in the tabernacle somewhat like the above. The boat got moved on its trailer with the mast folded down horizontal, but not lashed to the gallows. The masthead slid to one side, wrenched the tabernacle, and caused a split.

I put some epoxy in the split and sailed the rest of the season. Later I added some small 1/8th-inch aluminum plates at the top of the tabernacle in way of the pivot bolt:

PocketShip Tabernacle.jpg
PocketShip Tabernacle.jpg (1.16 MiB) Viewed 246 times


PocketShip #1's tabernacle is built significantly lighter than all production models (3/4" wood instead of 1"). I've been trying to get that tabernacle to tear off the bulkhead since 2008 and haven't managed it yet. And, in her new career as a PHRF racer, PocketShip #1 is now fitted with a considerably larger rig and subjected to all kinds of abuse!

Set up the shrouds so that the mast can't pivot forward and cantilever itself against the tabernacle, and you'll never have trouble.

PocketShip Racing 0619.jpg
PocketShip Racing 0619.jpg (166.7 KiB) Viewed 250 times
John C. Harris
 
Posts: 182
Joined: Thu Feb 05, 2009 12:39 pm

PreviousNext

Return to PocketShip Forum

Who is online

Users browsing this forum: No registered users and 4 guests

cron