Glass on wood II

[Puka]

The overwhelming concensus seems to not favour glassing over an old wooden hull.
Fine , if your old hull is well designed for its purpose and its traditional construction precludes
the use of epoxy/glass.
But if your hull is of an edge glued strip planked
configuration,that was not glassed at conception, surely this is the optimum solution?

What about the many cedar strip plankers that are laminated both sides in service today? Sure, a wood glass sandwich is potentially a moisture trap
therefore the integrity of the outer shell is crucial.
It seems it comes down to good building /glassing practices and frequent maintenance.

I have a 34' strip planker with several glue lines letting go just forward of the mast step. The result of over enthusiastic back stay tension,and poorly spread load from mast.
My current fix is dry to < 15% and a 900gm triaxial at 90deg to the strip plank and 3 coats of CPES inside. A lengthened mast step will be included.
Any suggestions/tips will gratifully received.
All the best for 2005!

[Scott Rosen]

Some folks a lot more experienced than me have suggested that the ideal fix for a strip-planked hull is to cold-mold a layer or two of wood over the hull, instead of glass.


This hull sheathing system, developed by the Gougeon Brothers of Bay City, Michigan, consists of overlays of plywood or cedar strips applied diagonally to the hull, and held in place with non-corrosive staples, while fully saturated in epoxy resin. Proper wet out and temperature/humidity control are essential to achieve a good bond. Sheathing should be conducted under cover, protected from direct sunlight and wind/weather. Details and specific guidance on hull preparation and the various methods of application of this method are provided in reference #5: The Gougeon Brothers on Boat Construction and #6 Wooden Boat Restoration and Repair.
From http://www.uscg.mil/hq/g-m/nvic/7_95/n7-95.htm

[JimD]

Just my uneducated two cents worth but the way you describe it it sounds like you have a mast problem first that has lead to a plank problem. If the mast load is pulling the planking apart no amount of fiberglass cloth is going to do much. Improperly engineered mast steps have been known to sink boats. You mention you are going to redesign or brace up the step in some way. I would focus on that, then make sure the planks are undamaged and properly reglued, then spend you're money on CPES and FG if you want to.

[htom]

What JimD said. Cure the disease rather than painting over the symptom.

[Puka]

Thanks Scott. Great site!
I had come across the cold moulding +/- 45deg method but feel glass would be more cost effective and quicker.Double diag. veneer is an attractive option though!

Thanks also to Jim & Htom, for the refocus.
We very nearly did the cheap and dirty fix. Quickly relaminate a longer mast step,temporarily caulk the glue line so we could continue racing!
But I hate doing things twice.

I cannot understand how glass would not add strength tangentially (in tension)to the hull where it is needed. (chainplate to chainplate around the hull). 900gm Triaxial is somewhat different to 6oz e-glass.

I intend to laminate a mast step similar to a bow (bow & arrow), from the b/stem terminating in the middle of the keel,reducing in laminations at the ends.

We have scraped the paint from the interior to the waterlne and found the timber to be in good shape. The odd bleeding fastening to be replaced and one frame that has rot around a keel bolt. Fresh water intrusion from the mast I suspect.
The timbers are somewhat dark (?), for Kauri with an moisture content (Lignomat probe) below the waterline of 30-->to 35%.Topsides are around 20%.Topsde colour is the typical golden colour.

I need an accelerated drying process, so I have a bag (huge) and hope to heat the thick timbers and run multiple de-humidifiers to hasten things.
(Assuming an edge glued kauri hull will stand the shrinkage)

Well,that is the current plan, no-doubt to be amended as we proceed. ~

[JimD]

I cannot understand how glass would not add strength tangentially (in tension)to the hull where it is needed. Puka, I wouldn't hazzard a guess as to how much glass it would take to provide the strength you need. Certainly it can't hurt. It just seems the fiberglass solution was looking at the problem the wrong way. Wouldn't mind hearing a little more about your boat. So far we know it's 34 feet long, so that narrows it down :D

[Puka]

Vitals
Designer : Bob Stewart "Patiki Class" LOA 34' WL 31' Fin keel, 2 tonne ballast.
Hull : 3/4"Kauri strip plank/epoxy edge glued.
keelson : 8"x3"Kauri
Keel frames: 21/2"x 3' Kauri solid @ 18" centres
Ribs: : 2"x 11/2" laminated kauri @12" centres, thru hull fastened (copper or bronze?)
Rig : Sloop, alloy mast/SS rig.
Main : Luff 37.5', Foot 16.5'
Mast step : spans 3 keel frames-glue separations centres coincide with front of mast step.
There is no significant movement in other visible seams/junctions/chainplates.
I will post an image of a gutted Puk,as much as it saddens me.

[ 12-30-2004, 01:56 PM: Message edited by: Puka ]

[Puka]

imagestation (http://www.imagestation.com/album/?id=2412440093)

[ 12-30-2004, 04:04 AM: Message edited by: Puka ]

[Puka]

Bump up--
Hoping somebody will see this thread who has "been there done that".

There seems to be a variety of fasteners used, some of which will have to be replaced.(Some of the steel screws have disintergrated)
What to refasten with, galv or bronze? Screws or rivets? Decisions, decisions!

We are just about ready to "kiln". That will be a learning curve in its self.

~~~ _/)

http://www.azom.com/details.asp?ArticleID=1102

[Dan McCosh]

Re: mast step loading. The problem stems from the very high, complex loads on a mast step. vs. the monocoque structure of the hull. A point loading of some 20-30,000 lbs. isn't handled well by any stressed skin, let alone fiberglass, which is poor at handling concentrated loads. The step loads have to be distrubuted somehow, either by a wider, longer platform, bulkheading to handling torsional loads, tension rods combined with compression beams, etc. The skin of the hull should mainly just keep the water out, not handle major concentrated loads such as a mast step. Those cracks are your hull saying "ouch".

[Andrew S/Y Rocquette]

Hi

I'm currently restoring my yacht Rocquette, who is a 30'6" walterline, 42' overall sloop, built in 1964 by Camper & Nicholsons. She's double glued carvel, total plank thickness a bit under 1 inch. Over the past 40 years (last 20-odd in the Med) drying cracks in the outer planking have cracked through the inner planking. These cracks have all been routered and splined and the hull re-faired. We're now going to veneer two diagonal layers of cold moulding over the hull mainly to add a bit of cross-grain strength, but also to add a bit of thickness. Only comment from the designer (Peter Nicholson) to this was a suggestion of adding 18 inches to the sailplan to compensate for any added weight. So this solution has my vote...! We're also beefing up the old corroded steel floors and metal ring frames by replacing them all with laminated wooden ones.

[ 01-07-2005, 05:28 PM: Message edited by: Andrew S/Y Rocquette ]