Best hull material for 65ft trawler

Im starting on an ambitious project to build a large trawler hull. I have the hull in mind, and I want to create the hull using aluminum tube as a frame, wrapped in fiberglass. I want to create a shaped hull surface in a 4ft x 4ft grid pattern of the square tubing in aluminum, and lay fiberglass around the entire frame. Im going for strength, low maintenance, and longevity. I am looking for reasons why this would be a bad idea. Aluminum not bonding to the fiberglass? Weight? Rigidity? Inconsistent thermal expansion? Any input is greatly appreciated.

 

What you are describing will not have strength, low maintenance or longevity. For those features, buy a conservative design in commonly available materials. If you want to design a large trawler hull, you should maybe take some courses first. In two or three years you will have a general knowledge. If you do a fair amount of boating, that will give you the practical aspect of it too. The forum has many threads of people deciding they will design a boat by themselves. The plans are the least expensive and most important part of the build. Also, as an amateur, you would have to spend several months to get a mediocre result. For example, how are you planning on finding the center of gravity or calculating stability and displacement?

 

So, a tube, which is a curve. Is then formed to create a shape. This adds double/complex curvature, unless you create an endless series of short straight line with all the parts welded together!!??
You will struggle to form the shapes you need and the ones you can, will locally elongate too much, as a %'age, and will initiate micro-cracks in the crystal matrix.
Unless your hull is box shaped - not recommended.

 

The mind boggles, how this proposed method of construction would proceed.

 

Sam, I think you'd benefit from looking up examples of the boat you have in mind and researching their construction. I know squat about 65 ft trawlers, but I'm going to take a guess and say you'll find either steel, and a lot of it, or thick planks over a lot of heavy timber framing. I'm pretty sure the steel would be cheaper and easier. Someone else here can correct me if I'm wrong.

 

It would be a 65ft skin on frame trawler.

Sam
As Gonzo points out, there is so many problems with your plan.
The tube spacing is orders of magnitude too wide. Until it is curred, fiberglass cloth wet with resin needs to be fully supported. It will sag out of shape if bridging a gap of more than an inch or three.

 

Sam, please listen to all the good advice above.
Please forget totally this plan of yours - if it was viable, somebody else would have done it by now.
Find a plan online for a trawler that you like, and buy it - the plans supplied will tell you how to build it as well.
Ignore these instructions at your peril.
And remember that the cost of the plans will be a tiny fraction of the cost of the finished boat.
Better to start with a good set of plans drawn by somebody with extensive experience, than to throw a million dollars into something that could easily turn out to be a complete disaster.

 

Because you'll spend a fortune and end up with a worthless pile of garbage.

Now, to the original question: STEEL

GOOD LUCK!

Edit: I love skin on frame, I've designed and built a few.

 

Buy a few books as a start.
Fiberglass boatbuilding for amateurs
Ken Hankinson $20.77 used at Abebooks.com

That shows a lot of ways that fiberglass hulls are made. Laid up in a mold, CFlex, "one off" methods for custom products etc.

Just remember that the supply side of composite has shrunk. Fewer epoxy makers, fewer re-inforcement sellers. This generally the price for composite is just increasing, unless you are able to get over-run materials from big jobs. Far more material being consumed by big corporations, especially aerospace and military than ever before.

 

Sam do you have any drawings, sketches, or even a 'scribble on the back of a fag packet' which you could share with us to illustrate what you have in mind?
Bear in mind that building a 65' trawler will take years of your life (working 60 hrs a week), and the cost of the materials and equipment alone will be in 6, maybe even 7 figures (in addition to the cost of your labour - you could be working somewhere else at a good hourly wage to pay for a ready made trawler instead).
Have a look on www.yachtworld.com and do an 'advanced' search - you can specify 'trawler', 'size', 'location' and 'price range' to start with - and see what comes up.
Invariably you will find that you can buy a boat that will meet your requirements, and it will cost a fraction of the material cost alone for a new boat.
And re your requirements, can you list your Statement of Requirements here re what you want this vessel to be able to achieve?

 

I just went looking on the yachtworld site and found some used, starting at about half a million. Those are all yachts, though, and we don't even know yet what Sam wants it for; he may be looking for a commercial fishing vessel.

I looked at four; two were steel (one a conversion of a commercial fishing vessel), one was fiberglass and I thought it was ugly. The last one was wood, and built of heavy timbers, frames and planks, so I guessed right on that. It was sale priced at ~$690K after a $70K discount.

 

A used engine with gears, shaft and propeller will cost him at least $14,000


Here is a 125' trawler for $50,000 Used 2019 Custom Explorer Vessel Conversion, 77554 Galveston - Boat Trader https://www.boattrader.com/boat/2019-custom-explorer-vessel-conversion-6996350/
A 1960 Marinette 60' for $99,000 Used 1960 Marinette, 20779 Deale - Boat Trader https://www.boattrader.com/boat/1960-marinette-5802454/

 

Looks like trouble from the 'get-go'
Add to your reasons it is a bad idea:
Hope you never get a lightning strike or serious electrical short. Rare... but they do happen.
On launching day you could christen it DISASTER (and, you won't have to wait for it to happen).