Hull Materials

[RubyBishop]

When going through the ‘for sale’ ads, one thing that hits home is the wide variety of hull materials used. The following list is from cruising type cats 30’plus:
=Duflex; =GRP; =Divinicell foam & Vinylester+Kevlar cloth; =Aluminium; =Strip plank cedar; =West Red Cedar/Glass/Epoxy; =Foam Sandwich; =Composite ATL Duracore/west epoxy.

. . . If your base requirements are safety and low maintenance, is there one material that stands out from the others.

[By safety I mean: can take a knock and be beached, without too much worry]

[sailingdog]

Cold molded wood composites like western red cedar/glass/epoxy or strip plank cedar are pretty low maintenance, as are cored composite fiberglass boats like divinylcell/kevlar/vinylester resin... There isn't any one material that is going to stand out.

However, cold-molded wood composites probably have much greater fatigue resistance than do the cored-composite fiberglass materials. A lot of people confuse the two fabrication techniques, since many cored-composite fiberglass laminates use end-grain balsa wood as a core material. From another post on multihulls, I wrote this:

Cold Molded Wood Composite

The first is what Chris White and the Gougeon brothers have done. That is cold-molded laminated wood composite construction. This generally consists of laying up multiple, very thin layers of wood and laminating them together using epoxy. The wood is often finished off by a covering of fiberglass to give it some added durability, but the bulk of the strength is in the cold molded lamination of the wood, not the fiberglass skin, which is effectively just a surface treatment.

Cold-molded wood composite boats tend to be very rigid and fairly light. One major advantage of cold-molded wood composite is the very high fatigue resistance that the wood construction provides. Properly built, these hulls are almost as low maintenance as a fiberglass hull.

Cored Fiberglass Laminate

The second is cored laminate construction. The most common core materials are PVC foams like Divinylcell and Airex, and end-grain balsa, like Contourcore. In this construction, the strength of the material is the fiberglass or composite skins, and the core adds to the strength and lightness of the laminate.

This is not the same thing as the cold-molded wood composite that I mentioned previously—the main difference being the thin veneers of wood used in the previous method are essentially encapsulated and thoroughly saturated in epoxy, which is not the case with cored fiberglass construction—where the resin is only used to bind the skin to the core material, but does not generally saturate the core material.

Highly loaded areas are often given additional strength via the use of carbon fiber or kevlar. The hulls are often given an inner layer of kevlar to increase the puncture resistance.

Many boats can be beached, if you're careful about it...but IMHO, the design of the boat is more important than the materials it is made of with regards to whether it is beachable. Most multihulls can be beached to some degree and many have very shallow drafts that beaching isn't actually necessary. Fin keel or strut and bulb keel type monohulls are probably the worst designs to beach.

Certain things can be done during construction to make a boat more impact resistant. If you're talking about cored-fiberglass composites, using a ductile foam in the hull rather than a rigid one and using layers of kevlar in the laminate both make the hull far more resistant to impacts. Kevlar greatly increases the puncture and abrasion resistance of a fiberglass laminate. It is also, often used to protect vulnerable areas on cold-molded wood composite construction in much the same way.

[RubyBishop]

Thank you . . . This is good information [I got a lot from your other articles to; one in particular was about the inspection trip].

Do you know anything about Duflex? I spotted a 38’ cat made from it and I am trying to do a little homework.

[sailingdog]

No, I'm not familiar with Duflex. The only Duflex I've heard of was an old camera brand, that was made in Budapest a long time ago....

[LookingForCruiser]

There's a long thread at cruiser's forums about duflex

Strenght of cats built with Duflex panel kits - Cruisers & Sailing Forums

[sailingdog]

Sounds like Duflex is a balsa cored pre-manufactured composite panel. Personally, I'm not a big fan of balsa cored laminates for the hull, especially below the water line. Minor damage to the hull's laminate either inside the boat or outside, can lead to the balsa core rotting with little indication of any problems until way too late.

As an example, a 49' SeaRay, which IIRC is balsa-cored, in my marina (yes, I know it's a powerboat) is a prime example of what can happen. The anchor rode locker drains were not properly installed, and allowed water to leak into the hull's core material. Last year, the boat was total lossed by the insurance company and the surveyor, doing a inspection drilled holes in the hull down by the rudders, and water poured out of the boat for days... almost the entire hull's core was saturated with water. Repairing it would cost more than buying a new boat. The insurance company refused to pay, because the issue was a pre-existing condition to when the current owner bought the boat, as the anchor well drains were factory installed.

[TQA]

[By safety I mean: can take a knock] IMHO there is only one material that will cope reliably with an impact at 6 knots and that is steel. I have seen a couple of steel boats that have spent a day pounding on a reef and were still watertight.


[and be beached, without too much worry] ANY boat fit for sea can be beached BUT beach anything other than steel on sand with a pointy rock in it and you are looking at a hole. ** Ask the guy who beached the Prout in Fishguard. }

OK I agree that no one in their right mind would build a smallish cat in steel as it would be too heavy and steel is not low maintenance but when you are reef dodging in Los Roques, hit a submerged object ot 6 knots or have a 40foot whale playing chicken with you; steel is really reassuring.

[sailingdog]

Originally Posted by TQA

[By safety I mean: can take a knock] IMHO there is only one material that will cope reliably with an impact at 6 knots and that is steel. I have seen a couple of steel boats that have spent a day pounding on a reef and were still watertight.

If safety is such a big concern of yours, why leave the safety of a shore-based life.

[and be beached, without too much worry] ANY boat fit for sea can be beached BUT beach anything other than steel on sand with a pointy rock in it and you are looking at a hole. ** Ask the guy who beached the Prout in Fishguard. }

Doing something stupid, like not examining the beach you're planning on beaching your boat on prior to doing so can cause troubles for anyone. I'd also note that a steel hull run up on to a beach will likely compromise the paint job protecting the steel from corrosion and lead to increased maintenance problems. That isn't necessarily the case with a cold-molded wood or fiberglass boat.

OK I agree that no one in their right mind would build a smallish cat in steel as it would be too heavy and steel is not low maintenance but when you are reef dodging in Los Roques, hit a submerged object ot 6 knots or have a 40foot whale playing chicken with you; steel is really reassuring.

A steel boat would generally also have a deeper draft, making it far more likely to hit objects, like reefs and such. Having an 18"-2' draft means that there are far more waters you can enter safely. This is a huge benefit when it comes to trying to find a hiding place from a tropical storm.

[RubyBishop]

If bad luck happens; then it is a matter of having redundancies in place. I guess with safety and taking knocks I am looking at my own ability and just know I am going to cockup and would want a material that is somewhat forgiving.
. . . Maintenance [cost / timing] is very important and will be a major factor

Beaching is starting to be an important consideration. I read an article about this chappie who said being on a cat with a small draft and mini-keels, he would look for shallows, and often during low tide would find the boat beached. With my disability and the fact I am going single-handed, I figure this could be a good ploy and could beach the craft periodically as a good safety net.

The main problem is finding a craft that has 80+% of what I want or need at a price I can afford.

[OsmundL]

Originally Posted by TQA

[By safety I mean: can take a knock] IMHO there is only one material that will cope reliably with an impact at 6 knots and that is steel. I have seen a couple of steel boats that have spent a day pounding on a reef and were still watertight.

I guess there are two ways to see the world: go sailing, or plonk yourself down on a small island and wait for continental drift.
Steel is popular in Arctic regions where you push through ice. Apart from that, alternatives are not so bad. As someone else said in a thread, I’d rather be upside down on a multihull that will still float. The Hummer approach ignores your greatest safety factor: the man behind the wheel.

[and be beached, without too much worry] ANY boat fit for sea can be beached BUT beach anything other than steel on sand with a pointy rock in it and you are looking at a hole. ** Ask the guy who beached the Prout in Fishguard.

Any? I suppose with a 6ft keel you could beach it, but don't have soup for dinner at the angle you'll sit there

In any case, steel is not “the only” – aluminium gets you there, and it has some qualities that make it more resilient in a crash. You mention 6 knots, and that is part of an interesting equation: Speed times Mass. The steel boat hits an object with more or less twice the force of a lighter fibreglass or aluminium body. Also, what hits first? If it is the keel and/or rudder as in most cases, those are the constructions I’d look at, and in that case a comparison of long keelers, fin keels and swing keels might be more to the point?

Construction is yet another factor. There are designs with watertight compartments, and some with inbuilt flotation.

Finally, there’s workmanship. Many steel and alu boats are home built, and you won’t know how good they are without solid research into the welding, surface treatment and dimensioning, not to mention the grade of steel or alu used.

I’d look at the whole package rather than fixating on a hull material. Does it have a reliable and well mounted engine? Are the couplings and gears sound? How protected is the propeller? Failure in any of these are likely causes of washing aground in the first place. Sometimes a relevant question with steel boats: is this a sailboat or a motor sailor? Does it have the rig and sails to haul you off a lee shore in an emergency?

Questions, questions, and so many answers