21Ft Tug, Corten steel?

Hi everyone, I've been lurking around here for a awhile and haven't posted much. Just trying to learn as much as possible here.
I've just finished lofting my new project, a 21ft Mal Low designed Tug.
I had considered building her in epoxy-ply, as I am a graduate of the old Bath Apprentice Shop in Bath Me, and have built several wood boats, so I'm comfortable in the material.
My plans for the tug are pleasure use in protected waters here in Florida. While I've done a little metal fabricationg before and some Mig welding, I'm leaning towards build her in steel.
Mal calls for Corten steel and my welding is amatuer at best as well as the cost factor.
Do you think it's necessary to use Corten vs, mild steel?
The scantling are:
Frames- 3/16" x 3 1/2" flat stock
Hull 3/16" plate for the bottom, 10 guage for the sides
Deck- 1/8" plate.

The hull is flat bottomed and straight sided. The frames are really just large rectangles. Here a few images and a builders model of the hull which should give you a good idea of the project.

Comments/Suggestions?
Thanks!

 

Steel Grade for Tug

robmill54,

Unless you ask the designer why some material was specified you can't be sure. If can ask you my find out a reason that doesn't apply to you, or you may be a contribution for that design element's justification in skill level, home building without forming equipment or welding ease.

Corten is just stiffer than more common plate/sheet and may have been specified to allow less experience builders/welders to keep the hull's panels more fair and smooth due to this material's increased stiffness.

I doubt that a 20-something foot boat made of 0.187" steel would need to be made of Corten steel! So I'm going to guess we can discount any added need for an increase of strength. All steel boats need to be blasted and painted till you are weak and poor, so I'll discount any corrosion resistance, which Corten only provides in outdoor projects on the beach and not as much immersed or awash in saltwater. It sure won't save any money- so that leaves me with the idea your designer wanted to give you the most smooth hull he could- resulting from you or any new builder working in welded steel.

Corten might be a good way to help this goal.

Make sure you go to the Glen-L site and read about the 'shrink-wrapped' welded steel tug boats they have there and see if those concepts can be employed in your boat. If you can understand this process then there is no reason to buy the more expensive - but admittedly stiffer material - just use wheel abraded and primered steel.

Just my opinion, and I may not have understood the designer's reasoning for calling out that alloy.

Cheers

kmorin

 

Thank you for your advice, I'll go to the Glen-L site and look at this technique.
Mal Low very unfortunately, has terminal cancer and is retired. He gives away the plans for free on his web site, and only asks for reproduction and postage. He can no longer respond to the endless questions on construction and I feel strongly that unless one has paid the full monty for the design that you are on your own from there, so I have not bothered Mal with the few questions that I have, and I respect his wishes not to be asked.
I think that with a welding course, a good Mig and a plasma cutter ( I want these tools for my "collection" anyway,that I have the ability to build her . While i realize that the hull itself is only a small fraction of the overall build, from what I've read Corten is difficult for an amatuer to weld and about 3 times the cost of mild steel?

It sounds to me that with careful construction and the fact that I'm not going to use her commercially, would land me at mild steels door.
Thanks again for your advice.

 

Tug Build

robmill54,

I'm sorry to hear about Mr. Low's health and understand that if someone gives their plans away that the support wouldn't be part of the package.

I'm not sure about Corten's actual cost but welding does require preheat and temp crayons to maintain the parent metal at certain temp to begin welding. So there is no reason I can understand for this tug to be in Corten unless the framing and hull panels were extremely light and you've already said they were not.

I agree that with a bit of training and some welding practice; a simple metal hull of this shape shouldn't be out of reach for anyone who has the determination to try.

Cheers,
kmorin

 

The whole idea of doing this in steel is overdoing it in my opinion.

This is only 21ft for goshsake - I have owned canoes longer than that. The sheer fiddlyness of the steel methods on a boat of this size makes me shudder.

The whole idea of a "mini" anything is that you can have the feel, without the expense. I bet you plan to trailer it around, so doing it in ply and epoxy makes a lot more sense to me.

But hey - you might want the welding practice on the new $1,200 machine you will have to buy. It would be a great new toy to practice on.

 

This tug was designed to be built in steel, it is an " option" to construct her in ply. If it's "overdoing it" thats ok with me. The whole idea of the "mini" tug is to have fun and enjoy myself at a slow speed and low fuel consumption.It's about enjoying myself, not the expense of the material.

The tug cannot be trailered because she has a 9'4" beam and I plan to keep her in the water.

As to my new "toy" , I'm interested in learning something new and developing skill in metal work.
Sorry if you are offended by my plans.

 

There you go - your decision is made! That was easy, wasnt it.

Now, just have a think about the type of steel and the type of welding gear, and you're away.

 

21 ft tug Pelikan

Hi there-- how is your build doing?..i realize that this thread is over three years old--just wanted to inform you Small tugs (tm) has now stopped suggesting cor-ten and instead suggests standard A36 mild steel plate.

Im building the Porker design... do you anticipate any trouble with the fantail plating?

Im using 3/16th bottom and 1/8th throughout...

pm me for details if your still building--and yea--do her in steel for sure...i love your model as posted btw...

 

pics of the tug in rhino...i have all but two frames built...here is a pic of two.