GRP, sandwich, Aluminium or steel??

I think I´d be quite open to heavily built epoxy GRP with foam core. It has quite some advantages over Aluminum or steel, but when you think you would have to do frequent hull repairs in remote areas (why should that happen? Do you run aground that often?) you might tend to believe in steel, probably in a rather religious way.
I´d also prefer the underwater surface to allow staying in tidal areas where some ports fall dry during low tide. So it might be nice if stabilizers are not the lowest part of the hull and the props and shafts are partially in a tunnel to keep them clear while sitting on the ship´s bottom and keel. At least for an explorer type passagemaker. For cruising the Med this obviously doesn´t really matter.

Don´t get me wrong, a heavy displacement boat will be a heavy diplacement boat no matter what material is used to build th hull. But with an adequate dimensioned GRP hull (epoxy please! And a yard that is capable of working with it!) you will get pretty much sufficiant impact resistance (think of the Farmont Trawler yacht that collided with a floating container on its way from the builder in Turkey to Düsseldorf Boat show some years ago, all they had to do was repainting some of the antifouling) while leaving out some galvanic issues and corrosion (especially corrosion issues underneath the isolation or in badly accessible areas inside the hull where most porblems seem to happen).
But the most interesting thing in a sandwich GRP hull is, from my point of view, that you can keep the displacement slightly lower with having the same load capacity and even get the same or better hydrostatic stability (using adequate ballast) as the hull and superstructures will bring less weight for same structural values. So you migth need a little les engine power for comparable results. Next aspect would be more affordable freedom in hull shape than with sheet material such as steel or aluminum which allows building a round bilge hull that is optimized for less wave resistance. So, obviously, a GRP boat needs to be designed as a GRP boat to benefit from the specific material dvantages! Not a design that can be built in various materials!

That obviously depends on the tech level the builder is capable of and the vessel size. Generally I believe that Airex/Herex foams would be the prefered way to go if the yard is capable of making proper use of it. You get more of the weight advantage and better noise and temperature insulation. But with a wood core, for smaller vessels you might get a price advantage depending on the yard of your choice that might compensate for the difference. Another aspect could be resale value as there is considerably less acceptance for wooden stuff in Europe, even if it is used as core material.

First of all I would go for a sailing or power sail cat.
If I had to go for a monohull in that size I'd opt for a steel hull with cored GRP super structure. I would never want a cored hull.

I believe that cored GRP is a good aproach for the size between 60 and 80 ft.
Above that steel might be a consideration.
And I would also like to understand why steel would be preferable for the smaller units.
Don´t get me wrong, I am in no way against metal boats, it´s just the thing that is not my favorite material to work with. So take my point of view with a grain of salt.
I have seen quite a number of steel boats I really liked. But from the tecknical point I have no idea why composite construction should be inferiour since strength and durability is not an issue + there are some advantages.
Then of course I know that a number of boaters believe in steel, some fellows even in a rather religious way.

Hi Willight,

At this moment I don't own a large boat as I don't have the time to enjoy it or do maintenance on it.
When I have the time to go cruising again I will go for a Wharram cat as in my avatar. This because I have been in maintenance long enough to appreciate simplicity and low tech systems. I would probaply want to cruise in the South Pacific and the east and west-coast of South America. The places I'd like to visit will be remote so key is that my boat can be repaired with minimal facilities at hand.

IMHO the worst enemy is draft, it makes you vulnerable to things you can't see like reefs, rocks, containers, whales etc. With the minimum draft on a Wharram and the use of sacrificial keels you could even drive the boat onto a pebble beach in order to do maintenance.
My second worst enemy is small compartments and in particular engine rooms. On a Wharram you can have a deck mounted single diesel that hydraulically drives 2 props mounted on a frame that you lower in the water when you need it and lift up when you're sailing. This reduces wear on the underwater parts, makes you less vulerable for groundings, you have very easy access to the engine and drive train and it's 3 holes less per hull.
My third enemy would be budget. Needless to say sailing is less expensive than motoring (when you make enough miles though) and low tech means low expenses on maintenance and replacements.
Further I don't like the heel of a sailing monohull and the rolling of a non stabilised power boat while on long passages.

I would like to choose a metal hull because it is simply the strongest and it'll keep its value. It is also more maintenance friendly than Aluminium in my opinion because it's easier to weld and a more common product that you could have repaired/ parts replaced nearly everywhere. Also less prone to galvanic corrosion. (imagine yourself accidently dropping a 316 bolt nut in the aluminium bilge and forgetting about it...)

As Wharrams are not designed in steel I'd obviously go for Bruynzeel marineply with epoxy glass.

I would never choose for a cored hull because the chances of having water ingress are in my opinion to high. Water ingress will affect the integrity of the hull. The fact that a trough-hull or a faulty installed port-light can affect the integrity of the hull is not worth the weight savings for me.

If I realy had to choose for a monohull powerboat I'd go for something like the Seahorse from Bill Kimley. Single engine, stabilizing sail, steel hull etc.
I'd prefer single engine over twin because of noise reduction, less maintenance, space savings etc. I would invest in a well thought out fuel delivery system with a good fuel polisher and spares though.

I also realy like the Dashew's boats. They pick the best from both worlds of sailing and powering.

Your statement sounds like your ideal of a passagemaker motoryacht would be George Buehler design. Nothing wrong with that. I like some of his ideas, especially the "Ellermaid" design loks like it could be fun.

Then, obviously the construction requirements and useable materials for a Warram are somewhat different from what would give sense for a 80ft. passagemaker yacht.

A quality composite hull has massive (coreless) areas for through-hull fittings and installations and so on which means that if the outer laminate surface is strong enough to ensure adequate impact resistance you should not have to be concerned about water in the core material. Of course that means to consider portholes, through-hull fittings and so on in when making the laminate plan.

I am a little irritated that you advocate steel and then you come up with your desire to do extended cruising in a glassed plywood Wharram. Concerning your propulsion concept I´d suggest to rethink the idea of a central engine with hydraulic drives, I believe ist might be a contradiction to your wish for simplicity. To me that sounds like a diesel-hydraulic outboard engine...

Hi,
If I were to build a boat and go cruising my choice would be a wharram for above mentioned reasons.
But (to stay with the original topic) my choice of hull material for a 60'+ powerboat would be steel.

When you have worked on a sterngland in a medium sized cat and you are 6'7'' tall you will understand my choice of deck mounted engine.