Slavishly copying commercial trawler plans for a cruiser

[makobuilders]

This inquiry is about the merits (or lack thereof) of using the design of a commercial trawler for purposes of building a personal cruiser. In my case I own a full set of design drawings for the boat which is an extremely heavy steel model with the following particulars: 50' loa, 47' lwl, 16' beam, 6.5' draft, hard chine, deep bilges, displacement 56 tons at D/L 540.

There is obviously only so much hard wood interior that you can have, so the extra 20+ tons (over a "normal" heavy displacement cruiser) would provide what advantages?

I have attached some perspectives that I created from the takeoffs but showing a radius chine version that I am playing with.

 

[TANSL]

Why do you need to copy a design of a steel boat?. This boat is designed to achieve features that probably has nothing to do with the boat you want. Do you design the ship you want, with the material you want.
Need a cruiser have a so big keel?
You may copy, if you like, the look of the boat above the waterline, with the underwater hull that you really need.

 

[DCockey]

.....

There is obviously only so much hard wood interior that you can have, so the extra 20+ tons (over a "normal" heavy displacement cruiser) would provide what advantages?

.....

Not advantages but differences include:

Increased cost of construction.
Increased fuel consumption.
Deeper draft which may limit where you can operate, where you can moor or tie-up and may increase cost of hauling.
​

 

[SamSam]

Is the reason for using these plans is to avoid buying new ones?

 

[Westfield 11]

To the list of drawbacks, add the need for a larger engine to push a wide deep hull, the difficulty and expense of finding a slip for a 16' wide boat in a marina as opposed to the fish docks and the fact that you would need to ballast the boat to keep from running near empty all the time. The sea keeping and comfort is very much affected by running such a hull without having tons of fish and ice in the hold as an essentially empty boat will have a very quick uncomfortable motion.

I suppose you could add extra fuel tanks and keep them full all the time like a tanker... Maybe you could make some money arbitraging fuel? I hear it is very cheap in Venezuela and expensive in America...... You could probably carry a few thousand extra gallons and the boat would ride on her designed waterline, although cement or water would be cheaper.

 

[PAR]

I only need a Mini Cooper, so I'm buying a Suburban . . .

 

[Westfield 11]

I only need a Mini Cooper, so I'm buying a Suburban . . .

It's more like "I have a dump truck already so how can I modify it for my daily commute into Manhattan.".

 

[Milehog]

Boat building materials and fuel are sold by the pound, kilo or whatever.
20 tons of boat + added fuel use will buy a shelf full of plans from top designers.

 

[makobuilders]

The points made above are all well-taken, but putting construction cost/fuel burn issues aside, how about a consideration for the advantages of a extra heavy displacement vessel from scratch.

Possibilities include:
* Extra heavy scantlings
* Extremely large fuel capacity (purchasing where cheap and in bulk)
* Extremely large freshwater capacities
* Ability to fit in water-ballast tanks to maintain stability as fuel is burned
* Ability to store tremendous provisions for long durations and bulk purchasing discounts
* The very deep bilges yield a vessel with lower profile and less windage

Would like some objective feedback to better balance pros and cons.

 

[TANSL]

Dear friend, you started talking about a cruise and now speaks of a tanker of high autonomy. Where do you want to get at?. You should define your LOR before wondering if a hull serves or does not serve your goals.

 

[kerosene]

* Extra heavy scantlings
* Extremely large fuel capacity (purchasing where cheap and in bulk)
* Extremely large freshwater capacities

Everything is a compromise. Is it a benefit to have sturdy scantlings? Yes can be, BUT its away from something else. Is it needed? same for the other points. Its bad idea to have features that are non essential as they will compromise other factors.

Tell us what do you want to do with said boat? Search for SOR on this site. Define the SOR and go from there - forget the existing plans for a second.

 

[kerosene]

LOR = list or requirements?
SOR = statement of requirements

we mean the same thing. Makobuilders be specific in what you want the boat to do.

 

[SamSam]

If it's ''an extremely heavy steel model'' boat, "the extra 20+ tons (over a "normal" heavy displacement cruiser)" doesn't necessarily give you 20+ tons more of capacity. Maybe you only get 5 tons more capacity (or 0 tons extra) and then you have to haul around 15 or 20 extra (useless?) tons of construction, forever.

I worked at a place that made 30' fiberglass boats. They normally took x amount of glass and 4 barrels of resin to make and were plenty strong for any intended use. An inexperienced laminator came along and made one and the boss went crazy when he saw the invoice for 5 barrels of resin. He thought the guy had stolen it, but the guy had just used too much resin and made a resin rich boat. The boss was still disappointed, because that was a monetary loss 100% out of profit, hence 100% out of his pocket, but what was notable to me was his comment that the new owner might as well have a barrel of resin bolted to the deck because he was going to have to haul that one around forever.

 

[Milehog]

The points made above are all well-taken, but putting construction cost/fuel burn issues aside, how about a consideration for the advantages of a extra heavy displacement vessel from scratch.

Possibilities include:
* Extra heavy scantlings
* Extremely large fuel capacity (purchasing where cheap and in bulk)
* Extremely large freshwater capacities
* Ability to fit in water-ballast tanks to maintain stability as fuel is burned
* Ability to store tremendous provisions for long durations and bulk purchasing discounts
* The very deep bilges yield a vessel with lower profile and less windage

Would like some objective feedback to better balance pros and cons.

I already did just that. You want to make a trip to save 30% on fuel with a heavier boat that uses 30% more fuel etc. Watermakers are cheap compared to the unnecessary burning of resources you envision.

Boat building materials and fuel are sold by the pound, kilo or whatever.
20 tons of boat + added fuel use will buy a shelf full of plans from top designers.

It appears you are either foolishly in love with those plans, too cheap to commission or buy proper plans which will save hunderds of thousands of dollars or a dreamer.

 

[Westfield 11]

Used boats are so cheap these days, why would you want to waste money building one? If you want an inappropriate fishboat hull, just buy a used one and modify it.....