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  Use of balsa-wood core construction materials in whalers?

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Author Topic:   Use of balsa-wood core construction materials in whalers?
jimithing posted 06-26-2002 10:52 AM ET (US)   Profile for jimithing   Send Email to jimithing  
Heard from a reliable source that older classic whalers were constructed with balsa-wood core decking componants. It was a common construction practice on many fiberglass boats in the 60's and 70's. I have a 1975 mako that has a fiberglassed balsa wood core deck that has developed soft spots in some areas. Apparently once the water touches this kinda of wood it will weep it up throughout the whole deck.....and thats the end. Short of cutting the deck up and replacing it, there is really nothing else to do.

I understand that it was used because of its lightweight characteristics, and inexpensive cost. Can anyone shed any light on the history of this kinda of wood being used in the recreational marine construction industry over the years?


Chap posted 06-26-2002 11:15 AM ET (US)     Profile for Chap  Send Email to Chap     
jimithing posted 06-26-2002 11:37 AM ET (US)     Profile for jimithing  Send Email to jimithing     

Thanks for the link....a very good and thorough history with good case studies.

John W posted 06-26-2002 12:15 PM ET (US)     Profile for John W  Send Email to John W     
I'd take Pascoe's articles with a grain of salt. While I agree with some of his opinions, his across-the-board dismissal of foam core construction is way off base. Obviously every Whaler that has ever been built uses whaler's own unique type of foam core construction, and they've proven to be the most long lasting boats of their kind ever made. There are plenty of excellent boatbuilders that have used & continue to use foam core construction with wonderful results; the custom builder Huckins Yachts, which has been building high dollar yachts since 1928, has used Airex foam core construction since the mid 1970's and still does today, and to my knowledge they have never had a hull failure of any kind. Intrepid Yachts use foam core extensively, and are incredibly well made boats...Pascoe has given them glowing reviews in his surveys, which runs counter to his "no foam core" mantra. Every 'glass Viking Yacht ever made has had balsa core hulls & decks, yet it is certainly a well respected builder. New Hattaras & Bertram yachts both use foam & balsa coring extensively to reduce weight.

Pascoe's assumption that builders use core construction techniques to save money is totally wrong for the most part, as in general, foam core or balsa core construction is more costly than solid glass construction, both in labor and in materials. Builders use cores to increase strength & reduce weight, despite its increased cost & complexity.

On the subject of balsa core decks, yes they can be a problem, I have a soft spot in the deck of my Mako. The problem is, a flat panel like a deck requires some type of coring to make it stiff, and that means balsa, plywood, or some type of foam core. You can't make a deck out of solid glass, it'd need to be so thick that it's weight would be a major problem. (The obvious exception here are smaller whalers, where most decks surfaces are the inside of the foam core hull, so a seperate balsa core deck is not required). There's not much of an alternative to some type of coring in decks, and that can occasionally lead to problems. But this is no different on a whaler than any other fiberglass boat.

bigz posted 06-26-2002 01:18 PM ET (US)     Profile for bigz    

Your reliable source is full of saltines!

On decked older Whalers glassed in marine grade plywood provided the structural integrate. Today I believe they use Whaler Board for this purpose.

JohnW, well said on Pascoe! My view/thoughts exactly, might add 3 marine surveyors I know thoughts to boot.


Chap posted 06-26-2002 01:31 PM ET (US)     Profile for Chap  Send Email to Chap     
Agreed, but Pascoe's article certainly provided a good point of reference to begin the discussion. Aren't the world renouned J sailboats cored hulls? My family's 1989 Shamrock's decks are cored with end grain balsa I think. They have not been compromised and are solid. One must maintain the integrity of the core, be it a Whaler or not.
John W posted 06-26-2002 01:47 PM ET (US)     Profile for John W  Send Email to John W     
Chap, just about every fiberglass sailboat ever made has balsa core decks & cabin houses, and many have balsa core hullsides. And the majority of them have never had a problem. You're right, keeping the core intact & not drilling holes everywhere is key. Avoiding large impacts on deck, like jumping down on deck from above, can also help prevent core delamination problems (and also gelcoat spider cracks).

Jimithing, the smaller whalers of the 60's had plywood under the fiberglass in places as bigz said, and didn't have seperate decks, and you almost never hear about rot problems with the wood in these older whalers. So your source is off base. I don't know what coring was used in decks on larger, later models such as the Outrages. But Whalers' lack of seperate decks and plywood cored stringers are two of the biggest advantages of BW construction over other well made boats like Mako's, Grady's etc in my opinion.

jimithing posted 06-28-2002 10:09 AM ET (US)     Profile for jimithing  Send Email to jimithing     
Thanks for all the responses regarding my post and for setting the record straight. Should have figured it out since whalers are totally foam filled.

I assume that if you have balsa decks....and many fiberglass boats out there do....then you really need to baby them and store out of the weather...something I have not done with my mako consistently over the years. Well, maybe if I dont have major balsa failure yet I can start storing out of the weather and stop the clock on some of the deteriation. We'll see.

bigz posted 06-28-2002 10:53 AM ET (US)     Profile for bigz    
As I mentioned the larger Whalers meaning Outrages, Revenge and the 27's used plywood during the 70's and 80's under the removable deck surfaces and cabin tops. As John W pointed out plywood was used in certain areas for reinforcement on the smaller Whalers. No balsa ever used that I know of in a Whaler.

Jimithing, if your Mako has spongy decks the damage is already done and will not reverse itself. You will have to rip it up and have it re-cored. I watched as our fiberglass guy re-did an Aqua-Sport I think she was a 20' repair a spongy deck area last winter and he mentioned he has had to do a number of older Mako's over the past several years. Sorry to say very costly, as it is labor intense.


thistle posted 06-28-2002 12:44 PM ET (US)     Profile for thistle  Send Email to thistle     
If the balsa problem is caught early you can avoid some serious repair costs. However, once it has gotten bad you can assume that the estimate to repair it will increase by 30-50% by the time the work is complete. It ALWAYS goes well beyond the estimated scope of damage. You end up chasing the problem before you know it. Most of the balsa used in decks cabin soles etc. is end grain balsa which has a nasty capillary habit like most woods. Long grain balsa or foam core material like klegicel are probably a good alternative but... as posted in this thread... get a sailboat guy to do the work and you stand a good chance of getting a much better and less expensive job. This is old hat to sailors.

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