new boat questions

[texasair]

I am getting specs together for a new aluminum boat that I may have built.
It will be similar to a c-dory, about 24' long 7'6" beam. Twin 60 Yamahas on brackets with a full transom.

I am considering mounting the brackets at the widest points. From the rear the outboards will look like they are mounted on a catamaran. I would have the swim step and folding ladder mounted in the center, between the motors.
I am open to pros and cons of this idea vs mounting the motors in the conventional location, close together at the center of the transom.

2nd question....Pros and cons of an aluminum tank for potable water?

Thanks Brats.
Tex and Sharon

[Wandering Sagebrush]

Tex, why not just buy a CDory? I suspect that it would be a lot less expensive than having a custom boat designed and built.

Are you prepared to deal with corrosion issues? I was looking at an expensive, used semi custom aluminum boat here on the Oregon Coast and noticed several areas of corrosion lifting the paint. The asking price on this boat was well into the 6 figures. I used to think I wanted one, but after seeing the corrosion on about that was about two years old, I don't think an aluminum cruising boat is going to be in my future.

[Barry Rietz]

The past year I gave serious consideration to the same idea and would certainly like to know if you will "copy" the Toland lines, or have you something similar from another naval architect? As for the engine placement, putting them as far apart athwartship gains some real advantages. One is that you will be able to turn the vessel within its own length in close quarters manouvering. The disadvantage would be if you lost one engine (crabbing), or if the design calls for a "deep V" under body requiring longer "legs" to maintain submersion in rough going. The use of 5000 series marine grade aluminum is a great material for water tanks. It would be nice to see the vessel design posted with either photos or line drawings.

[C-Otter]

How about the noise : engine noise, water noise underway and water slap on the hook. I have found this amplifled on a aluminum boat. C-Otter

[Wefings]

Out of curiosity , do you have an aversion to fiberglass or another more direct way of asking is why aluminum ? Will this be a work boat ?Your motor plan will create guaranteed cavitation in turns if you plan on being able to operate on plane .
Marc

[NORO LIM]

Spacing of twin engines can be complicated. Variables include size of engines, design of hull, and needs of the individual user, at least. Here is a discussion of the subject with respect to twin engines on Boston Whalers.

http://continuouswave.com/whaler/reference/twinEngineMounting.html

Weight distribution, "crabbing" badly when using only one engine, or shaft length exposed below the hull line in the case of a deeper V, as noted, are all potential downsides to wide spacing. I think fuel efficiency, top speed, and general handling at speed may all be less than optimal with engines on the "corners." I would be wary of real wide spacing on a single hull design.

I'd definitely talk to someone who knows more than I do about the subject - and there are lots of folks who can step over that bar.

[texasair]

Marc, You win, I had not thought of the obvious. I was just thinking that the wide spacing works on cats and that it would give better low speed handling for docking, etc. But cats stay fairly flat in turns where a mono hull banks like an aircraft, therefore picking up the outboard engine.
So both engines back to the center of the boat.

Any thoughts as to aluminum working OK for potable water?

Tex

[Doryman]

I've never read of aluminum being used for water, fuel or waste. Most are plastic or cast iron (on big boats.) I'm sure someone will jump in if that is not correct.

Warren

[journey on]

The fuel tank on Journey On is aluminum. I believe it's also baffled, since it carries 100 gal.

Because of external corrosion issues, I would think that plastic would be better, though it might be hard to get baffles inside.

Early Catalina 36' sailboats (diesel) had corrosion issues and they changed the location of the tank. I've seen aluminum, iron and plastic in that boat.

Aluminum and fresh water should go well together. Judy bought some aluminum flasks for hiking. As for waste tanks, at least the smell wouldn't come through.

Aluminum boats should be lighter than fibreglass boats. An equivilant Kingfisher is listed as lighter, and more expensive.

Boris

[Captains Cat]

Warren, the fuel tank(s) on your boat are aluminum, as are mine.

Charlie

[Will-C]

Hi,
I would have a spot built so a standard plastic 20 gallon water tank like the ones C-Dory uses could be dropped in place like into a rack or bucket type mount. It won't rattle, it will be easy to clean or replace as long as you design the mount right. All standard stuff. You can see the water level and if it's fowl (green) just looking at the tank. RV antifreeze will not hurt it to keep it from freezing. my 2 cents. C-Dory Venture models use aluminum fuel tanks also.
D.D.

[Nunya]

As DD says... go with plastic for drinking water. Less chance of getting Alzheimers from drinking out of aluminum. Aluminum fuel tanks are pretty much standard in boats.
The question was asked "why aluminum?"

Pros
Aluminum is lighter
Tougher. (Banging into the dock, loading on trailer, beaching,etc)
Easier to add brackets, etc. (Just weld them on)
Easier to repair.
A lot less maintenance
And most of all... don't have to worry about getting core wet.

Cons:
Colder in northern waters
I don't know, but they are probably hotter in southern waters
Sweats a lot more than fiberglass
Noisier
Can't get the flair or nice looking lines that you can get from a fiberglass mold.
Just my opinion. I've owned both.

[Matt Gurnsey]

I will argue the "tougher" point a bit.

We have had some used aluminum boats here, and all have had small dents and dings from docks. What amazes me is that potential buyers look at the boat and are put off by the dents.

I was at the point with one guy I wanted to yell "That's what aluminum does! it dents!" He was just going on and on about the couple of dents in the boat. Hey, if you want a perfect boat, buy new, used aluminum boats have dents.

But the incidents that caused these dents would not have left a lasting mark on a glass boat. Plus, a glass boat can be repaired, and with a good glass guy you'll be hard pressed to find the repair. A welded aluminum repair will always be visible.

Each material has it's strengths and weaknesses. One of the biggest advantages to aluminum is that a builder doesn't have to invest tens of thousands of dollars in molds. The aluminum boat can be designed, cut and welding can begin. Which may be why so many aluminum builders popped up in the last 10-15 years. There was little initial investment in starting up a boat building business.

Plus fiberglass never acts as a sacrificial anode in salt water environments. Just sayin.

[Sea Wolf]

And another thought:

One can repair fiberglass at home with common inexpensive tools, and make modifications in wood and add them to the hull.

To repair aluminum, or modify it substantially, one needs an inert gas welder, which is somewhat of an investment, plus a developed skill in using it. Cutting larger pieces of aluminum can also be done easier with the right tools.

Just one more facet to add to the discussion.

Joe.