Small Steel Workboat Design

You won't be going any faster than 5 knots. If that isn't enough, you have to re-consider whether this is worthwhile.

 

Mr Efficiency
I think your right, as much as I'd like to build this boat, I'm coming to the conclusion that it's not going to be practical for my purposes.

I spoke to a colleague today who years ago built a simple 16 ft steel workboat.
It was flat bottomed curving up to a shallow angle 4 ft from the bow,
He said it was easily pushed with an 8hp, and with a 20hp it would plane!

I'm going back to the drawing board. Will draw up some designs and make some models.

Still intending to build using 3mm steel plate.
I'm thinking 15 ft long, 6 ft beam, double chine, flat bottom with a slight dead rise towards the bow, flared sides mid ships.
Maybe something like the flats boats they use in the U.S.A, only heavier and slower

 

Why don't you just go and buy an aluminium one? At least here in Australia there are plenty of boats like that, they are pretty tough, cheap and will plane with enough HP.

You could buy 3 and wear them out before you equal the price, if you put *any* value on your time, of making your own, to your own design, from 3mm steel plate. Not to mention the ongoing maintenance, which is going to be extensive for steel and virtually zero for ally in this size range.

Think about it - slam a piling, chip the paint, rust bleed until it's touched up. Run up on a shore, scrape the paint, instant rust bleed until it's touched up. Etc etc all the bloody time.

I like making stuff, I do it all the time, but there are limits.....

PDW

 

Hi PDW
The reason I'm intending to build from steel is
Firstly

the price, I can buy the plate for £350
An Ali boat of the size I need will cost me £1500 minimum
I already have plenty of epoxy paint, so corrosion needn't be a problem.

Secondly, I work with steel a lot, maintenance is easy for me, I have the right tools, and a crane on my boat so I can work on it easily.

And last, I love steel as a material, I work on steel boats often (albeit larger ones. It has immense tensile strength, much more than Ali.
It's easier to work and repair.

I accept many of your points, they just don't really apply in my specific circumstances.
However, if I wasn't an experienced steel worker, didn't have a stock of epoxy and had plenty of cash to spend, then I would agree with you completely

One more thing, I love making things!

Thanks for your feedback though

Oz

 

Is this boat intended for mostly smooth water ?

 

Then there's the sand blasting, the stringers, pipe and all the other fiddly bits....

So less than 5X your guesstimated price for the steel alone. Sounds like a bargain.

This might work if

a) you really don't put any value on your time, both for the initial build plus the ongoing maintenance.

b) you are happy with a displacement vessel and its 5 to 6 knot speed or you're going to install a bloody BIG engine to get a small and grossly overweight boat on the plane.

I have a lot of free epoxy paint too and I'm building a 12m steel sailboat. I like working with steel. I understand that bit.

But for a 5m punt type boat, I'd just go and buy an ally one because I could put the many, many hours of the initial build to a large number of other uses.

PDW

 

yes, mostly smooth water. It does get choppy sometimes, so it would have to be able to cope with that when necessary, its not that often though.

Im thinking that I should build a displacement hull, In my limited experience, they are better in a chop.
Is this correct?
Also using less hp to get around would be an advantage.

My concern though is lack of speed, I really need something capable of 10 kts.

I know this is probably going to sound a bit insane/stupid, but for years I have been reading about the viking period ships particularly the Gokstad ship.
They must have been quite heavy, but fast and obviously efficient.

So how about,,,,, wait for it,,,,,
15.5ft Length, 5.5ft Beam, the hull geometry roughly based in this type of design, but with more beam in relation the Length. coming up to a squared off bow, and the aft becoming flatter toward the stern, ending in a flat transom, so can be pushed effectively with an outboard.

Probably sounds mental, please advise me if it is, as im about to spend several hours drawing it up.

 

Atkin's boat plans have some smaller steel vessels you may have looked at. If someone held a gun to my head and made me build a small steel boat, I'd be looking at something roughly similar.

 

As far as many, many hours is concerned, building a simple steel utility boat wont take me that long, I spend I large proportion of my time fabricating various things from steel, for me its the quickest medium to work in by far.

 

Hi Oz,
roughly speaking in displacement mode you need a waterline length to waterline beam ratio of 6:1 to become a "slippery" easily driven hull & "break free" of wave-making resistance issues.... the narrower= less waves, there's a little more to it because surface area increases so skin friction goes up, then there's also the possibility of planing, for this when the boat's "up & running"/planing the surface that is supporting the vessel must generally have a positive "angle of attack", this means that the back end of the boat(the bottom) needs to be running down towards the transom & the transom is pretty much the lowest point of the "body" of the vessel.... there's plenty more to it but at the size if you want speed your going to have to get up on top & boogie.... which equals some more power, & buttock lines that fall not rise towards the transom when the boats running.

A Viking style hull might plane/surf in "some" conditions but are relatively skinny & shallow easily driven hulls.... not a 3:1, I worked on a Gokstad replica last year, the Vikings had some cool innovations! the boat I worked on was very directionally stable & we could push it at low speeds with very little power, earlier in it's life had sailed to better than 20 Knots as the story goes...
Jeff.

 

Sounds good, once the plates are developed & cut & you have a spare set of hands to push & assist, that size boat should be stitched up by lunchtime on monday(if longti joins are plate to plate) & welded out by the end of the week..... then the "details" take up some more time. The mig I use will deposit about 12-14 meters an hour on a typical "smallish" fillet weld at well under it's duty cycle, of coarse I only ever achieve about 2-3-4 meters an hour on boat work because you move around a bit & grind out some cold starts/whatever.
.....not that I've done that in a few years though
Jeff.

 

I quite agree with this bit, it's why I'm building a steel sailboat. Compared to mucking about with epoxy/ply, steel is a dream to work with. Fit up, hit with a weld, move on. No waiting (and waiting and waiting) for epoxy to kick.

However, it's *heavy* so for a boat of the size you're talking about, with the plate thickness you're talking about, you're buggered on the speed.

Make it longer and displacement hull speed goes up.

Make it lighter and getting it to plane becomes feasible.

I simply don't think that there is a good solution to your statement of requirements.

PDW

 

PDW
"I simply don't think that there is a good solution to your statement of requirements."

I starting to think that you may be correct, Im very much hoping that your not though.

Im thinking that maybe Im trying to get too many things from 1 boat, especially a small steel one!

So, Ive had a think and narrowed down my criteria to what is essential for me, at least in the short term.

1. Stability, I frequently carry a heavy cargo up to 500kg's. So for loading/unloading etc, it has to have good stability.

2. I need to achieve 10 kts, this is partially because the tide runs fast in my location, and that I often use it to commute several miles.

3. It must be very, very, strong and have excellent abrasion resistance.
My environment is harsh, obstructions under the water, steel piers with no fendering, often mooring against decaying steel and concrete river walls, etc

If you "all" think that it is not possible to get these 3 things from a 15 ft steel boat, then I will accept the advise of people on this forum who are obviously more knowledgeable than me on boat design. I will then not waste any more time on it, and have to come up with a more expensive solution (both in time and money).

On the other hand, If it "is" possible to get these functions in a steel design then I can afford to replace my current boat, which at its current state of decay, maybe has 2 months left before its un-usable.

 

Hi Jeff

Wow, id love to work on a Gokstad replica, that must have been fascinating.
What timber was used? did you use traditional iron fixings?

In your opinion, am I wasting my time trying to build something which will not perform as I need it too? 10 kts etc?

thanks again for your help
Oz

 

Hi Oz,

The Viking vessel was built late 80? planking/framing Douglas Fir with plenty of Jarrah also. Fastenings were copper.The work we did to it was more essential repairs & "dressing" for use in an exibition
Jeff.