Opinions about Cored Hulls ...

[Mike OReilly]

My good old boat (circa 1977 -- Taiwanese-built) has a cored hull below the water line. It is Airex cored. I have never heard of any problems with Rafiki hulls.

Build and design quality probably matter more than whether a boat is cored or not.

[Dockhead]

Originally Posted by minaret

LOL! On this website alone there are countless stories of people dealing with rotten saturated core. I'd say at least 50% of the people here who have owned cored boats have experienced some sort of core problem. That's not a good track record. Sea Ray was a drop in the bucket, core problems are legion. Talk to any pro boatyard worker. Coring hulls below the waterline is just not smart. I'd say that's the source of most "anti-core stories", owners who have had to pay tens of thousands to fix the problem. And there are lots of them.

All of the core problem stories I have heard relate to old boats from less than high end yards, in fact IIRC all the stories related to U.S. and Taiwanese built boats of the '60's and '70's, particularly C&C's. I have never heard a single story about core problems with Swans, X-Yachts, Hallberg-Rasseys, Malo, Sweden Yachts, Baltic, Contest, etc. Maybe someone else has, but I haven't. Except for Oyster, you almost cannot buy a high end, non-production GRP yacht made in Europe which does not have a fully cored hull.

[Dockhead]

Originally Posted by Don Lucas

Well that's not true. My Hunter's hull is cored above the waterline and solid below. Far as I know they have been dong it that way for some time!

Should always be real careful about using the word "always"

Yes, sorry, I meant below the waterline. I expressed myself poorly.

AFAIK, nearly every boat in the world built in the last 30 years is cored above the waterline, and has cored decks.

[Dockhead]

Originally Posted by Dockhead

Yes, sorry, I meant below the waterline. I expressed myself poorly.

AFAIK, nearly every boat in the world built in the last 30 years is cored above the waterline, and has cored decks.

Apparently there are a few boats with solid topsides -- apparently Beneteau doesn't even core topsides. But that is surely rare.

[minaret]

Originally Posted by Dockhead

All of the core problem stories I have heard relate to old boats from less than high end yards, in fact IIRC all the stories related to U.S. and Taiwanese built boats of the '60's and '70's, particularly C&C's. I have never heard a single story about core problems with Swans, X-Yachts, Hallberg-Rasseys, Malo, Sweden Yachts, Baltic, Contest, etc. Maybe someone else has, but I haven't. Except for Oyster, you almost cannot buy a high end, non-production GRP yacht made in Europe which does not have a fully cored hull.

I've worked on plenty of HRs and Swans with core problems. Most of the rest you list have not been around long enough to see many examples. Obviously newer methods like SCRIMP make all the difference, but the vast majority of boats out there were not built in the last ten years.

[svrodeorm]

Lots of opinions here, but where are the facts?

I am no expert, but I can relate my experience, and some facts at least.

Facts: cored fibreglass (airex or other closed cell preferable to balsa ME thkinks) are among the stiffest hulls around, and also the strongest pound for pound, next to cold molded. This is good IMHO.

It is an expensive method of building hulls, and the work force has to be very well trained and skilled. This is why relatively few (if any?) big producers build cored hulls.

Own experience: I owned a Laurin 32 for 5 years. Built in Sweden in 1965 with airex cored hull and deck. Out of 215 or something built between 1964-1978 I've heard of 2-3 with water penetration problem. In at least one of those, whole sections were cut out of the outer skin and core replaced and then reglassed. A big job for sure, but not that much worse then a major 'blister job' below the water line. I suspect (but do not know for sure) that those few boats had thru-hulls made by owners and not sealed preperly, otherwise the problems should be more common I think.

I now own a US built (Bristol, Rhode Island) Southern Cross 35 cutter built in 1984, also with Airex cored hull but balsa cored deck.Handlaid of course. This boat, nad the bigger sister SC 39', were built about 40 of each before the builder, CE Ryder, went bankrupt around 1990 IIRC. Most likely due to these boats were too expensive to build at a time when the big 'manufacturers' started 'building' boats with the labour-saving use of spray guns of sorts to spray a mix of resin and cut fibreglass into the molds.

I do have serious doubts as to the strenght of any hull built with this method and considering that the cost of a hull is just about 20-245% of the finished boat, there's not a shadow of a doubt that if I were to look for a new boat, in GRP that is, it would b cored for sure.

I hope this will cast some light to this matter for anyone contemplating buying a cored boat. Look out for,and carefully inspect, any owner installed thruhulls and of course bad repairs from collisions of whatever but that goes without saying.

If installing a new thruhull, for a watermaker of whatever, the usual rules are to be followed plus that the core should be ground out a couple of inches around the hole drilled, and then be replaced by thickened epoxi. Not a daunting prospect for a reasonably apt owner.

Fair winds

[noelex 77]

I agree with those who express reservations about cored hulls.
Problems are not common, but they are very serious when they occur.

Cored hulls are attractive to boat builders. Foam core is cheap and the lighter hull weight means less expensive ballast, smaller mast and fittings.
Less so for cruisers stuck in out of the way places with delamination problems.
Just my 2c.

[Cheechako]

There are a lot of cored hull attempts out there. I have no issue with cored topsides as long as nothing penetrates the core. Problems abound with cored hulls. There was a Taiwanese boat called the Celestial 48 (or was it the 51?)cored every where. They were all so badly waterlogged they couldnt be sold. Havent heard of one in years, not sure if they still exist or not.

I'm surprised to learn from the post above that the Rafiki is cored hull...? If you havent found it waterlogged... my bet is you havent looked hard enough!

Sabre, Freedom, C&C and various cats have cored hulls for many years in some way or another. Many of them have issues.
The newer core hulls may have a good chance of surviving with the recent technology used. But personally I would run from anything older with core below the waterline...problems abound. I tried to buy a C&C Mega 30 a couple years ago just for racing. There are absolutely none I could find without a waterlogged hull. every one is... unless it's already been fixed.

[Tortuga's Lie]

I guess I'll chime in on the subject regarding my experience. My Tartan 37, built in 1977 has a mostly cored hull, meaning that it is solid glass in areas of stress such as the turn of the bilge, and cored in large panel areas. These hulls have a very thick outer skin (1/2") and then the layer of balsa added then topped off with more glass creating a hull thickness of well over an inch in most areas. I would say that this yields a very stiff hull that has a layer of insulation due to the balsa. I have owned the boat for 18 years now and can honestly that I have had no issues whatsoever regarding the coring....I really don't even think about it until I read these threads I have not had any moisture issues or delamination. Several of these T-37's have circumnavigated. I could imagine maybe if you were to have an impact penetration that the laminated hull would be a pain to repair, but perhaps since it is laminated, the impact may not be as catastrophic as a thinner, solid GRP???

[Cheechako]

I would imagine most people wouldnt know if they had a waterlogged hull until they sell and the survey finds it... It sounds like your Tartan was built similar to my CT44. Very thick hull with core addded also. With a thick hull, I guess it really doesnt matter if the core is wet... except when it comes time to sell. The other unmentioned issue with cored hulls is the fiberglass shrinking away from the core (not bonded to the blasa/airex). Here again, if the hull is thick, not an issue really, but if the design is relying on the rigidity of the core crossection, could be an issue.

[Mike OReilly]

Originally Posted by Cheechako

I'm surprised to learn from the post above that the Rafiki is cored hull...? If you havent found it waterlogged... my bet is you havent looked hard enough!

It's hard to prove a negative Cheechako. Other than drilling holes all over the place, I'm not sure what else to say. No signs of any water intrusion into the hull. No flexing, no cracking, nothing... The thru-hull I replaced revealed a core perfectly dry and stable. I've not heard reports of any Rafiki hulls with problems. None. If you have evidence of problems with these hulls, I'd certainly love to see it.

[Cheechako]

So you are saying that the thru hull was through the core? That's what worried me.... especially with a Taiwan boat. I like their hulls, but I've not found them savvy enough to worry about penetrating the core properly, and their sealants seem to give up after time. Glad you dont have an issue.... Always liked that boat, but never in a million years would have thought it was a cored hull.... learn something every day!
a 3/16 drill bit thru the inner layer of fiberglass (inside a cabinet etc) will tell you.... That's how I located the limits of the coring issues on my partially cored hull. The bottom line though is your Rafiki is probably built so thick on the outer hul, that the coring doesnt matter that much!

[Mike OReilly]

Originally Posted by Cheechako

So you are saying that the thru hull was through the core? That's what worried me.... especially with a Taiwan boat. I like their hulls, but I've not found them savvy enough to worry about penetrating the core properly, and their sealants seem to give up after time. Glad you dont have an issue.... Always liked that boat, but never in a million years would have thought it was a cored hull.... learn something every day!
a 3/16 drill bit thru the inner layer of fiberglass (inside a cabinet etc) will tell you.... That's how I located the limits of the coring issues on my partially cored hull. The bottom line though is your Rafiki is probably built so thick on the outer hul, that the coring doesnt matter that much!

Thanks. I may try a few holes, but so far I have no reason to suspect any problem. I have a copy of the original blueprints for the boat. I can see (and it was confirmed when I replaced the thru-hull) how the hull was laid up. It specifies the number and types of glass cloths used. The lower hull is very thick -- so much so that I had to use a long-shaft transducer just to get through.

I certainly can't comment on other Taiwanese-built boats, but I'd have no hesitation in recommending a Rafiki.

[Bash]

Originally Posted by Dockhead

Inexpensive production boats like Bene, Jennie, Bav, Hunter, etc., are always solid fiberglass.

High end monos like Swan, Hallberg Rassey, etc. are almost always fully cored, with Oyster being the notable exception.

I don't know about the others, but Hunters are solid fiberglass (with kevlar reinforcement) below the waterline, cored above. I understood that this was becoming an industry standard.

[Dockhead]

Originally Posted by Bash

I don't know about the others, but Hunters are solid fiberglass (with kevlar reinforcement) below the waterline, cored above. I understood that this was becoming an industry standard.

The Kevlar is unusual (and expensive), but otherwise that's SOP for production boats. High end boats, not only in Europe, but also Hinckley, use balsa cores throughout, including below the waterline. These days using SCRIMP or other methods to infuse end grain balsa blocks with resin.