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Old 19-09-2016, 18:37   #1
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Hull thickness comparisons

Hello every one,
Been reading and learning from this forum for a while very good source of info. I have a question can't seem to find much on Google search about it. What are some typical hull thicknesses for say boats such as dana 24 's, flickas , Allegra 24, cape dorys, nor'sea,bristol channel cutters,albergs,sea sprite,etc? Also is there a way to find the thickness of a hull short of drilling holes or removing through hulls? What would be considered a "thick" hull? Im trying To get my head around what The boats that are considered from the " classic plastic" eras hull thickness are, and also trying to determine what a safe thickness would be for off shore work. Thanks for reading
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Old 19-09-2016, 19:56   #2
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Re: Hull thickness comparisons

G'day, & welcome!
Thickness isn't a measure of quality or soundness for going offshore nearly so much as is the quality of construction in general, & in her layup.
Not too long back, it was common to have hulls of some boats made with a chopper gun. Which is a spray gun that literally sprays bits of chopped fiberglass & resin into a mold in order to make a part. It's quick, takes much less skill to use, & until recently, was the cheapest way to build something in fiberglass... But, the quality tends to be low, as there's about 2x more resin used than glass. And no glass with continuous fibers are used.

Then there's your basic hand layup, still using polyester resins. Going back to when glass first was used in boats. And usually it layers of mat, alternating with woven roving, layed into a mold.
The resin content's lower than the above, but still high. And the hulls still tend to be seriously thick. With them being stronger than chopper gunned hulls, but still "low".

Then you move up to something using stitched & woven fabrics, like tri-axials, unidirectional, biaxial, etc. Using any of the 3 common resins, & either laid into a mold by hand, or laid into a mold & vacuum bagged until things are cured. The latter being more common in custom boats. And the more high tech the construction & materials, the stronger the layup. With a higher cost, & they tend to be thinner hulls, though things are often cored as well.

From there you're in the realm of infused hulls, using usually Vinylester, or Epoxy. Axial, stitched, woven, & exotic fabrics (Carbon, Kevlar, etc.). Cores are common/prevalent. And hulls sometimes get "baked", aka Post-cured.
They're the strongest, & often lightest. But most expensive, & technologlically labor sensitive. Though for custom boats & parts, are the way to go.

How thick a hull is will depend on it's age, type of construction, materials, intended useage, etc. With their not being a stock answer. As a hull made of vacuum bagged epoxy, & high quality fabrics can be 4-6x as strong as a hand laid hull made from polyester resin, & cheap fabrics, thickness per thickness, or pound per pound.

In older boats things are a lot thicker, as they didn't know how strong GRP was back then, nor did they have tools like FEA. Plus resin was cheap compared to now, or even 30yrs ago. That, & modern boats depend as much on their structural cores, bulkheads, framing, etc. for their strength, as they do on their glass skins. Where such wasn't the case 30yrs or 60yrs ago.

To some degree, hull thickness can be ascetained by tapping. And in a survey you might ask them to pull out a through hull for inspection as part of checking a boat out. At which point you'll have an idea of her thickness at that specific point. But hull thicknesses vary Widely thoughout a given boat, depending on what kinds of stresses that area of the boat will see.

As for example, in my Ranger 33' she was several inches thick in some places near the keel & in areas which supported the keel. While in others she was 1/8" thick. Like in her topsides, back aft by the cockpit lockers & quarter berths. With her being a "mid-level" boat quality wise from her era.

You'll have to get a feel for what boats are higher quality for their age range. And gather that they're solid. But there's no easy answer to the question. Nor are many boats inherently weak in their hulls, but more so in other ways that they were built. Such as in bulkhead attachment for example. It being a major contributing factor for & of this.

One easy to see example of it might be to look at the reports of which boats survived beachings in the big Cabo storm of approx 1980, & why. As some were barely scuffed, while others were totalled, by the 'same' conditions.


PS: And yes, your reading of Ferenc Mate will to some degree help, especially with pre 1990 boats. For another excellent perspective, download (gratis) the Dashew's Cruising Encyclopedia Vol II at www.setsail.com along with the rest of their books. Just don't try & read it all at once
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Old 19-09-2016, 20:03   #3
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Re: Hull thickness comparisons

Quote:
Originally Posted by Eastward ho 24 View Post
Hello every one,
Been reading and learning from this forum for a while very good source of info. I have a question can't seem to find much on Google search about it. What are some typical hull thicknesses for say boats such as dana 24 's, flickas , Allegra 24, cape dorys, nor'sea,bristol channel cutters,albergs,sea sprite,etc? Also is there a way to find the thickness of a hull short of drilling holes or removing through hulls? What would be considered a "thick" hull? Im trying To get my head around what The boats that are considered from the " classic plastic" eras hull thickness are, and also trying to determine what a safe thickness would be for off shore work. Thanks for reading
Most blue water vessels built before 2000 have thicker hulls than most current builds. Especially compared to the the volume builders. These early vessels were over built in terms of laminate schedule.

We've recently replaced a number of thru hulls in our Liberty 458. Hull thickness ranges from 3/4" to over 1/1/4". No delamination is evident. Delamination is more important than thickness in terms of latent defects. Latent defects are the biggest concern in composite structures.

Composite thickness is no guarantee of quality. Thicker hulls do suffer much less 'oil canning' and consequently less seperation of interior components. This is the main benefit of these older vessels.

However the older vessels have less stiff interior structure such as the underfloor grids. Most of these grids are built of timber. Modern vessels tend to have much better engineered composite grids.

Nearly all current vessels are optimized to minimize build costs. This means they will be less restorable over time. Thinner laminate schedules lead to more deflection based fatigue.

Strain based fatigue tends to occur at much fewer cycles than stress based fatigue. In some cases strain failure will occur at just a few thousand cycles. Auto pilot mounts failing on a neighbour's hunter is a typical example of strain failure.

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Old 19-09-2016, 21:44   #4
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Re: Hull thickness comparisons

That's a good answer UNCIVILIZED.


I read somewhere that when they started building glass fibre boats they intuitively laid them up to the same thickness as the wooden boats of that era.


There is no doubt that light boats go faster for the same rag in the air and the use of cores to increase the panel stiffness allows some incredibly light and stiff boats to be built from composites but their fatigue lives and impact resistances tend to be considerably lower than the older solid layup boats.
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Old 19-09-2016, 22:12   #5
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Re: Hull thickness comparisons

Quote:
Originally Posted by Eastward ho 24 View Post
Hello every one,
Been reading and learning from this forum for a while very good source of info. I have a question can't seem to find much on Google search about it. What are some typical hull thicknesses for say boats such as dana 24 's, flickas , Allegra 24, cape dorys, nor'sea,bristol channel cutters,albergs,sea sprite,etc? Also is there a way to find the thickness of a hull short of drilling holes or removing through hulls? What would be considered a "thick" hull? Im trying To get my head around what The boats that are considered from the " classic plastic" eras hull thickness are, and also trying to determine what a safe thickness would be for off shore work. Thanks for reading
Welcome here! First off there is a classic plastic social group and owners there may be able to help you out.
Cruisers & Sailing Forums - Plastic Classics
The boats you mentioned all have a good reputation for "thick" hulls. First of all the early boats' hulls were not only thick but hand laid up roving and/or mat. Secondly where in the hull are you talking about? I have one of those thick-hulled early boats, mine is mostly roving. My friend with his Cheoy Lee has a hull laid up with more mat according to Lloyds specs back in 1970 or so. His boat, at the through-hulls is about 3/4" thick, but that is from my memory and I wish I had measured it now. My old Columbia 24 was very stout and as I recall the thickness at the through-hulls was around 3/8" and my current boat, a '62 Columbia 29 is also stoutly built but I have not yet pulled a through-hull. My boat was built at the same time as the Bounty II (later evolved into the Rhodes 41 and Reliant) and the first builder did get tips from the guys at Aeromarine in Sausalito who were building them in 1960. Later Glas Laminates took over and I think they kept the same lay-up schedule but I'm not sure. I did show a photo of the deck thickness in one of my albums though. I did also fill a hole in the topsides that was about 1/4" but I didn't measure it. I can't think of any way to measure it without looking at a hole for a through-hull though. There is a good collection of photos of a refit of a Pearson Rhodes 41 that shows a through-hull removed and the hull thickness measured.
https://www.facebook.com/barry.bucha...1&l=54dcd7dc0b
The comment on the photo I added pretty much says it all.
Contacting the builder, if they are still in business could help as would owners groups. All the boats you mention have active groups I am sure. Early Columbias were all built well and there is an active users' Yahoo group. Good luck and let us know what you find!
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Old 19-09-2016, 22:19   #6
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Re: Hull thickness comparisons

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That's a good answer UNCIVILIZED.
Thanks

I read somewhere that when they started building glass fibre boats they intuitively laid them up to the same thickness as the wooden boats of that era.
This is my understanding as well. And from what I've seen of some of the early gen. glass boats, it's pretty much true.

There is no doubt that light boats go faster for the same rag in the air and the use of cores to increase the panel stiffness allows some incredibly light and stiff boats to be built from composites but their fatigue lives and impact resistances tend to be considerably lower than the older solid layup boats.
On cored composites. If they're properly done, especially using some of the cross linked, resilient foams, the impact resistance is very very good. At times much better than other structures. Though it does depend on the design, materials, & strength of each. As well as the type of impact(s).

The biggest drawback, other than needing more experience needed to build these boats, is eventual water intrusion into the laminate. As nothing is waterproof. But I'd take a well built foam cored boat any time, assuming she was lovingly cared for.

I'd do the same on a solid glass boat too. With the same caveats. As they're not immortal either. Having pulled off plenty of tabbing, & other old glass, by hand strength alone. As various tabbing, & other non-primary chemical bonding having had failed over time.
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Old 20-09-2016, 03:42   #7
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Re: Hull thickness comparisons

Greetings and welcome aboard the CF, Eastward ho.
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Old 20-09-2016, 04:18   #8
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Hull thickness comparisons

As has been pointed out thickness is not necessarily an indicator of strength nor quality.
But thickness can be very accurately measured non destructively with an ultrasonic thickness gauge if you really feel the need


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Old 20-09-2016, 05:32   #9
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Re: Hull thickness comparisons

Thanks for the bounty of info. The hull I'm talking about is a 77 eastward ho 24. Portsmouth yacht co built them and as far as I know they're out if business. They commissioned C.e. ryder to build the hulls and I believe c.e. ryder has a pretty good reputation for quality. I'm pretty sure it's hand laid up fiberglass I can see the matting in places.it has a hull liner which limits my views in most places. The hull is in great shape from what I can see from the bootstripe up gel coat looks perfect. When I painted her bottom I didn't notice anything however I didn't really know what to look for. Hull to deck joint is lapped over with fiberglass ( I assume ?) To bond them then the toe rail is bolted through that. Im just trying to gauge where this hull stands in the realm of high quality boats like the ones i previously mentioned. I never see the Eh 24 mentioned in the pocket cruisers or small blue water searches I've done but the numbers seem to suggest that it's a pretty capeable little boat, on par with the ones I've mentioned?But then again I'm new to sailing. Done lots of Google searches regarding the Eh 24 nothing much on them. I'm trying to figure out; with the right modifications (rigging,chainplates, conpanionway,seahood.) If she would be capeable of extended passsages and assuming I did my best to time weather windows, and obviously gained more experience at the tiller. I know people have crossed oceans in canoes if the weather's right and I know smaller boats will be more uncomfortable. I'm just wondering if weather kicked up and I was caught in it if this design would keep herself.o nice again thank you for all your knowledge
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Old 20-09-2016, 05:58   #10
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Re: Hull thickness comparisons

Looks like it's another overbuilt plastic classic.

EASTWARD HO 24 sailboat specifications and details on sailboatdata.com

http://www.boatbuilding.xyz/sailboat...ails-well.html

http://www.sailnet.com/forums/genera...d-ho-24-a.html
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Old 20-09-2016, 06:41   #11
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Re: Hull thickness comparisons

Yes I've read that,it seems that's about all I could find in my Google searches. As for the hull Inquisition, I think what started me questioning the hull thickness is I can see light through the topsides mainly in the bow ( as there is no liner present there). It's not painted so I assume for a white gelcoat this would be normal?
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Old 20-09-2016, 06:45   #12
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Re: Hull thickness comparisons

I'm thinking that's quite normal.

I can see light here and there on my boat also (Bristol 27) and on all my lightly built beachcats that had hatch covers on the sterns
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Old 22-09-2016, 07:24   #13
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Re: Hull thickness comparisons

As I recall, the end of the sixties and on through the mid seventies, there were a lot of experimentation and corner-cutting going on in the boat building industry. The cost of material rose and the economy, especially all things related to the petrochemical industry, declined. Chopper-gun construction was bad enough. But in some yards, everything from fire-retardant chemicals to talcum powder was added to the resin. As a general rule, I am very cautious of plastic boats built anywhere near the 1970-75 range. On the other hand, I'm no expert.
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Old 22-09-2016, 09:06   #14
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Re: Hull thickness comparisons

Ok thank you every one. Messing around with the coach roof from the inside it looks like the hull liner may be attached to the deck using chop gun method ( I only guess) at the bow where the deck joint and the liner ends if I get my fingers up there I can feel the strands. I poped out a port light and there I could clearly see deck and the liner with no filler between at the boat it's different though. I'll have investigate further
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Old 22-09-2016, 11:04   #15
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Re: Hull thickness comparisons

Left--good post.

I will add that cored hulls can be devastatingly problematic. One in particular had an integral holding tank which, once it failed, pumped gallons of raw sewage throughout between the hulls delaminated skins, due to panting action.

Hull piercings must be very carefully dealt with.
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