building a 25 ft Tug

ya Tugboat...Ive got a fabulous newspaper picture...1960's. The town I grew up in had a fuel tank farm. Twice a month a smaller fuel tanker would come to fill em' up. The day the ship arrived I was Tugging around the docks catching crabs. Had to move off the dock and stop crabbing while the ship docked. Soon as the ship got tied up I went back to crabbing. Rather than drift around off the dock, I tied a line from my minitugs stern to the fully laden ships anchor . The current was running a bit, so it stretched me and my mini tug away from the ship. A photographer from the local newspaper was walking the waterfront and took the picture. From the angle it looked like I was towing the ship. Picture made it onto the front page of the local newspaper..
TugBoy to the rescue !!! Guess I was about 9 years old. The picture is framed at my moms house.

 

Oh and on top of my general tugging, I was also engaged in a bit of survey, undersea recovery work with my mini tug. One season I was tugging around close to shore and rammed into a submerged piling. My Minitugs quarter inch plywood hull got punctured and we sank like a rock. Dad lifted her up the next day and instead of patching the hole with wood, he used a sheet on clear plexiglass. Minitug sonar. I was frequently called in to perform critical undersea searches for lost fishing rods and shoes. Very Profitable buisness.

 

Thanks Micheal. I had a small hydroplane i had built growing up. 10 ft - with a 20 hp hurricane merc! very fast.
I wasnt on the ocean but it was a large and prominent lake--to me it was joyous freedom. Many a yarn growing up- my best freind also had one and we teamed up to wreak havok and become the stuff of legends!!...
ahh i sure miss those days

 

Hi Bert-Ill probably just weld it up with 6011 or 7018 rods simply because I dont know and also stainless rod is more expensive...How did the machine work go for your parts?? hope they did a good job for you...

 

Hi Larry sorry for the late reply--Just so you know the tug is fresh water based on the great lakes- mostly lake huron and Georgian bay(oh what beauty!)...

won't see any seawater but its designed for 3/16th plate or even 10 gauge--mind you he calls for cor-ten- but i wonder if that plate is lighter than standard alloys?
and I just went through all the rigamoral of trying to resize another vessel doing just that--messing about with the plate sizes....it throws off all the stability doing that. now im just sticking to the deisgners scantlings...the weight came from the plans as specified by the N.A.
geez-I thought the tanks were integral tanks on this design??.i could be wrong--ill go look at the design again. im sure you could easily build in tanks to suit. this is what is nice about these plans. I cant post them but you can see most of the same info almost on the website www.smalltugs.com, he has some really nice designs-

although i am lowering the bulwarks by 10 inches. so i can jump on and off the boat without tripping over them...ill be doing this alot. as well- it makes for a bit easier towing work with lower bulwarks. Ill use a tow span as well...very true you dont want the stern awash in a tow or backing...
sounds like you did a lot of work on fishing vessels?- were did you sail out of?
cheers!

 

tugboat...you stated now that you will actually be using the boat as a tow boat, that means commercial and also that you have to build to survey, no changing plans mate if that is the case.........

 

Sorry Landlubber--just a miscommunication mate...I might be using it for light duty commercial work- but just for under the table stuff, like moving someones vessel or anything that someone asks me to do "off the log".--i probably wont get it surveyed but if needed ill build it to proper scantlings. In this case Ill build it exactly to specs from the designer n.a. ...these plans are done to loydds or ABS. etc...for commercial cetification. im guessing its a nasty thing trying to get certified...so many rules...

 

...no worries mate...understand

 

does anyone know if corten a 242 is lighter than common mild steel?

 

Cor-Ten A & B are members of the HSLA family of alloyed steels. Cor-Ten A is ASTM A242. you'll find that it has a higher strength as compared to the same thickness of mild steel. I can't remember the Cor-Ten B ASTM designations, but will look them up for you. As you move up in carbon content & add alloying material, weldability & forming become issues. A242 hasn't been the panacea in marine applications that was previously expected and must be as well protected as mild steel. Michael Kasten addressed the use of Cor-Ten, here: http://www.kastenmarine.com/alumVSsteel.htm

and there have been a few discussions of it's use on these forums. There are other alloyed steels which have received a percentage of nickel and chromium to increase corrosion resistance, but availability and cost are issues you'll have to consider. "Ad hoc" and "Mike Johns" will be able to advise you on the advantages/disadvantages of using HSLA steel for your project, better than I can. My initial reaction is that you probably won't want to spend the extra $.

(addition: I should have re-read the Kasten article before posting, as he lists the ASTM designations for Cor-Ten A & B and other HSLA.)

 

To directly answer the question, no it's not. You will not find any significant difference in mass per m3 of the various steels. The only way to reduce the mass is to use thinner sheets which therefore need different metallurgy to get to the specified materials properties.

Thinner sheets are harder to weld fair.

PDW

 

This then --is good news for me..thanks PDW!
i notice Colvin and some tug designs indicate a242 for thier hulls...i did a bit of research on the net--some say that it can be used without blasting etc..others say its not better and has to be blasted anyway--to me then-its more practical to go with pre-primed...ill look for the oiled and pickled steel...

 

I discussed this with Tom a number of years ago. The 2 advantages of CorTen steel were higher strength so you could reduce plate thickness and somewhat greater resistance to corrosion so a bit more forgiving of paint chips etc. Flip side, more expensive and somewhat more difficult to bend. Weldability about the same IIRC. It has to be blasted regardless if it has mill scale on it.

In your case I'd just go with A36 plate. It'll be fine. Pay extra for pre-primed or pickled & oiled if you have to, it'll still be cheaper than blasting. I just got some plate back from the blasters and localised overheating has caused some plate distortion. Fortunately you can move 4mm plate quite a lot with hydraulics as long as you leave at least 2 edges somewhere to move to. Only took me 3 hours to fit this plate (3m x 1.3m).

PDW

 

thats a good sized plate--well done- even though im not sure if thats fast or slow snce I haven't plated a hull yet...im assuming thats fast since it seems like a big plate...forgive my inexperience here..
im really interested to see some construction pics--if you have them...
You boat is considerably bigger than mine. at 25 ft, I hope to plate it with bigger plates..i cant remember though -is your deisgn a single chine or double??...i have even seen multi-chine mono-hulle sailboats...one at 30 ft.
how well do these fair? as far as the pre-primed--yea--that seems the way to go ...i hope its not too much more per plate but since my build is now 25 ft rather than 40-it'll balance out in costs...

 

It's fast for *me*.....

Plenty of multi-chine and radius chine sailboat hull designs about the place. Tom's heavy displacement family (TAMARACK etc) are double chine hulls. I might build one of those sometime in the future.

I might post some photos once I've got the plating finished.

PDW