need help with plans

Anyone out there know about adapting plans for a steel tug to ferro cement?...I believe in ferro as a solid (and not obsolete) material...IF it is done right. My issue is that I have great plans for a 45 ft steel tug (designed for the us navy 1943-1950's). I cannot figure out some things:
1. what is the knuckle in the table of offsets? 2. why are there more frames than stations??? this one i have been trying to decipher for a month but to no avail(o.k. don't laugh). So anyone have any idea why there are more frames than stations? there are only offsets for the stations but the construction plans show a lot more frames than there appears to be offsets for...there is no info missing i am just not getting it. hope someone could help...

 

Stations usually run FP, 1, 2, 3, 4, 5, 6, 7, 8, 9, Midships, 11, 12, 13, 14, 15, 16, 17, 18, 19, AP. These are used to define the hull shape in the linesplan and when you loft the boat. Frames are where structural frames are located for the boat. They don't need to correlate to the stations. You could draw a boat with 10 stations that had 59 frames if you wanted to. I built a rowboat with 10 stations and 3 frames.

I don't follow the knuckle -- is it just a knuckle? Sometimes tugboats have knuckles. It's easier than bending the steel, and it doesn't cause a significant increase in resistance if the knuckle is aligned parallel with the flow over that part of the hull.

 

Thanks for the feedback

Hi Bito, thanks for replying, i hear what you are saying about the stations, but that leaves me with the problem of building the frames. if there are more frames than stations how do i figure out how the frames are developed?
Would i need to loft the lines out to full size and then get the frames from that info? seems to me that would need a heck of a lot of space and money to build a loft floor? i would not even know how to begin to lift the frames from what is given...anyway i am a little confused. there are some frame details in the construction plans but only about half are shown...what i was wondering is if i build it in ferro, would i need the same amount of frames as in steel? then i could just use the stations as frames and build the counter stern from the construction drawings?

Regards

Doug

 

Regarding frame spacing -- You can't just take a construction plan for a steel boat and use cement -- you need to get a qualified naval architect to actually go through and determine how to build the hull. I agree that the lines and the arrangement may be great, but you can throw the construction plan in the trash.

Regarding the lofting -- lofting is the fun part!! You can get the offsets of the frames pretty easily. If you don't have a 45-foot floor to loft the boat on, you can do it to scale (1/4 scale should be accurate enough, and I could do that in my dining room) You can also use a computer program like Rhino. You essentially draw the boat in three views, using the offsets in the offsets booklet. Then you draw lines where your frames are supposed to be in the profile view and top view, and measure the offsets from those two views. It's not that tough of a process and there are many books that explain it fairly well.

May I ask -- are you actually planning on building this boat? Do you have a boatyard? Do you have the $$? Why do you want a tug boat? Even though the boat is cement, it's still going to cost a bit to make a 45 foot boat, and you're going to need someplace to build it.

 

Tugboat:
I think it's better to digitalize the forms, do the hull fairing (based in the available sections in the forms plan), by using a devoted computer program and then take the needed frames profiles from there. But you have to take into account that usually forms for steel boats are drawed "out members" or, in other words "inside the skin". Ferrocement forms are rather drawed "out skin", so there is a subtle diference and you have to provide for it.
To know where the frames, bulkheads, stringers, etc. have to be located, you need to perform structure calculations for ferrocement first. As Bito says you should contact an NA with experience in that material.

 

I know that Rochester Marine Design would be able to throw something together fairly easily if you were interested in going forward with the project. I'd contact them.

 

Tugboat:
You'll find intersting articles on ferro construction at:
http://boatdesign.net/directory/Designers/Design_Articles/
And more info:
http://www.ferroboats.com/

 

Knuckle

I saw this link only today.
Generally, in Naval Arch, Knuckle is the joining of the straight line bottom to the staright line portion of the side of the hull. In steel construction The CHINE form (That is knuckle) has two staright parts, the bottom of hull and the side hull are staright parts joint at the knuckle. This is free of curvatures. So cionstruction becomes easy.No bending of plates. In ferro cement you need not follow knuckle. Ofcourse you can. But need not.

Adapting steel to Ferro needs to have modifications in the plan.The weight and the center of garvity changes.

 

Well, it depends on design. There are steel boats with no chine. Most round steel forms can be adapted to ferrocement, just taking in account the skin issue previously mentioned.

 

hey everyone-sorry its been so long since i posted on this thread but it took me this long to get a big enough place to build the boat. ok so- the design is a round bilge design 45 ft army /navy st tug- a 1943 US Army design, their size came about as being the maximum length that could be transported as a unit aboard a railroad flatcar of the period. Mass-produced for the war effort, they served both Army and Navy, designated as YTL by the latter. Several are still in service with the Navy.
dimensions- 45 loa, beam 12.5 ft, depth 6 ft.
the hull is beautiful one of the nicest workign platforms i have ever seen wioth low freeboard stern for working lines...do any pro-ferro-cement advocates think ferro-cement could be used as a viable alternative in working commercial operations if built strong?...and what about getting a commcercial inspection..would it pass?....the only other thing i could do since i cannot afford 1/4 inch plate , is to buy 3/16 plate and ballast it a little more...

what are steel advocates ideas on using 3/16 rather than 1/4 inch?...i personally dont think the stability or characteristic of the hull would be much f a problem using slightly lighter guage..

with ferro i could use thick hull forms which could make it very strong...

btw im starting a new thread using this post as my beginning since its been so long since i have replied...look for it if you think its worth reading the posts...

 

can't believe ive put this off for 4 years- got sidetracked by my sub project. but want to just "do it" ... Ive since figured out everything about the build. I have decided to build in steel..ive costed the steel out at aprox 7000.00 plus some extras. I am going to loft out to 1/4 size. then have the drawings reproduced to actual size.
And i amn not going to use 1/4 inch plate as in the scantlings for the hull plating. yes- its going to be lighter...and yes its goingt to throw of some characteristics of the vessle but i doubt the effect will be great and i will compensate with extra ballast below.
but thats better than being heavier. using the legendary
cat d318 marine (NA) w/ mg 61 3:1 gear turning a 36 x 34 steel prop. this was running well in a 40 ft tug before i got it. i expect the build to take about 3 years.

and hopefully as stupid as this sounds, i hope were still around in 2012 long enough to enjoy it. my guess is fossil fuels will be gone soon, and we prolly dont have much time left to enjoy our current use of those fuels...

 

I suspect steel is a safer bet than ferro in this case.

Your tug probably had very low freeboard as designed, and cannot afford to be heavier in a new incarnation.

Many ferro cement hulls are heavier than their steel equivalent, and if this proved to be true in your case (and you built to the exact same lines), your ship would float deep, have insufficient freeboard and thus insufficient stability.

However, you should be careful about changing the plate scantlings from 1/4 (6.35mm) to 3/16 (4.7mm). This is not because of overall weight characteristics - you are correct that you could ballast to adjust for lighter steel weight. It is more to do with other things.

The thin plate does not give much impact resistance for workboat duty and is harder to weld without distortion. More importantly (especially since you seem to want to work commercially) you may struggle to get the "new design" approved by ABS or US/Canadian Coast Guard or whoever controls your commercial operation. The originally specified plate thickness went with an original design of frame spacing and frame size - change one element and other things will have to be looked at as well.

Also, having said all that, why not buy a second hand steel tug hull of the type you like ? In the present climate there should be a few around - sold out of the USN. No use for you, but over here in Europe there are one or two old Dutch tug steel hulls around - some in good condition.

 

Thanks Jr MacGregor,

i appreciate the response. I know it sounds nuts, but im so picky about deisgns. I wanted a boat that has beautiful lines(in my opinion). and i love this tug.
The issue for me is- in order to buy a tug hull i have to get a loan. I really would rather just invest my "loan" payments each month and not pay interest and build the boat as i go. Yes a loan would mean using it sooner- but i have lots of time to get it right. also i looked at many hulls- and most would cost as much to recondition as to build. I saw one thta needed complete replating and it would have cost me the same to build from scratch and it wasnt really the nice design im looking ofr. i guess it comes down to what i really desire for the characteristics. also I really wont be doing much commercial work..i just want to have a tug- and be different than others. so there wont be the day in day out requirements of a commercial vessel. i may occasionally help unground a boat under the table for a small fee. but thats about it.

can you bend 1/4 inch plate the same as 3/16 using pad eyes and come alongs? to a radius bilge?

 

Not to become a killjoy, or to discourage you, but allow one question please, tugboat.

Are you aware of the cost you will have to stem all the way down to launching?

It seems you work on tight budget, which can be done. But too tight a budget, or underestimating cost, always ALWAYS, ends up in desaster.

All the best for you, your family, and your project.

Take care.
Richard

 

thanks Richard, Yes , there is a great amount of money involved. the steel alone is about 8000.00 cdn.

sadly, It will take me three years to finish this project start to finish- just to launching stage, and there will still need work to be done on it. After studying so long and going back and forth on so many ideas--i just got tired and started the build since lifes too short to keep searching for the perfect boat, , this boat is probably too big for my needs. but it is the ONLY boat I like as much as i do..tomorrow I take my plans to a steel yard to help me cost out the steel.
they will see the construction details and hopefully give me a clear idea. It is winter here so i will have to erect a temporary shelter too.

Richard--maybe you can help: i am not sure if its better to build upside down or right side up?..any ideas on which would be better?
i was leaning towards right side up..but seems plating might be easier upside down?