Small Steel Workboat Design

340 kg seems an underestimate to a 3mm plated boat of this size. I'd have thought nearer to twice that. It is not going to matter much for a slow boat though, unless you are dragging a submerged transom around you thought would be clear of the water. If your boat when loaded turns out to be much heavier than the design specs, it is in additional transom drag you will be most penalised.

 

Looks like the search is over..... thats a pretty good head start, length wise maybe just cut back to a raked pram bow but .8m is probably too much.
15 hp is heaps for displacement mode vessel of that length.
Jeff

 

Fantastic, I want one too!
Jeff.

 

Mr Efficiency your correct, I did the calcs after a very long day!
448 Kg's.

Anyhow, plans are now redundant now I've seen the levlievlet.

All I need to do is to decipher the plans into English and work out
How to shorten it to 4.5 meters

 

Dunno mate, I'd hold my fire for a little bit, it is a sailboat, not a work boat. You really want a near-plumb bow to maximise your waterline length, and I doubt more than one chine is warranted for your purposes.

 

Essentially, you could use the same geometry for the hull but add a "wedge" to the centerline to increase beam & cut the bow back to a raked pram bow, the "wedge" need not come to a point though & be "sawn off". Is there some advantage re registration or such to restrict the length to 4.5M?.... you could reduce the length also above the waterline at the transom with a vertical transom. Where I live there's plenty of "box" punts with an angled swim end used as work boats, some of the smaller ones are great to work out of as standing/kneeling/sitting in the bow gives very low freeboard & the opportunity to access other floating structures close to their waterline.
A shortened & widened Dutch Scout boat would be a pretty effective low HP commuter boat to access waterfront worksites & vessels with a load of tools & material & plenty good for water & groceries, with the current speeds you've expressed, some simple application of Seamanship & working with the flow(patience) as you've also implied.
Now you have a design, best to get on with it, nearly been a week now..... it's a dinghy!
Jeff.

 

Mr Efficiency
What is the difference between a sailboat and a workboat?
My main concern is safety, ie stability in choppy water, also when loaded up with weight.
Do you think the levlievlet would not be a suitable craft?




Jeff, I know Im taking my time, after all 1 week and no boat to show for it, "Lazy"!

As far as speed is concerned, Im reconciled to the fact that the boat I need will not be fast.
Im wondering what the hull speed of this design is, any ideas?

The reasons id like to shorten the design are, the aft deck on my Tug is approx 17ft x 9 ft
and I would like to build the boat on my deck so I dont have to pay to use another premises,
Also, I am looking for a different mooring for my Tug, so will probably have to pay to moor a dinghy alongside, they charge mooring fees by the ft here, I can hang a boat up to 15ft on davits on the stern, any bigger then its really got to stay in the water.
Having said that, I am not ruling out a bigger boat.



Thanks for your suggestions, I am going to try and work out how to shorten it, maybe build as per the plans, and just shorten the stern by 2 ft?
What do you think?
also, why do you suggest increasing the beam?

 

Simply wider = more stable, longer at the same beam generally = more stable too
A wedged or parrallel plate of 100-200mm width added at the centerline gives more space & load capacity & your outboard should still push it fine.

 

15 hp is enough power, but the mounting on a displacement craft is not so straightforward. Ideally you would have the extended leg versions that allow you to have the leg well submerged without creating excessive drag, that is difficult with a standard engine. You don't want a situation where the prop will leave the water in rough conditions, which is likely if you mount the cavitation plate level with the bottom.

 

Well... there is also a smaller version! It's probably just too small at 4 by 1.6 m and 350 kg. Capacity is "6 young scouts". It's called the "junior lelievlet" or juniorvlet.

http://bds.home.xs4all.nl/juniorvlet/juniorvlet.pdf

Maybe you can interpolate somewhere between the two?

-Thomas

 

I'll just add that I got the plans from this website http://bds.home.xs4all.nl/index.htm

There is an interesting series of build photos for the juniorvlet. http://bds.home.xs4all.nl/juniorvlet/page_01.htm

-Thomas

 

Thomas, thanks that's very helpful.
As you suggest maybe I could try to find a medium between the 2.

Mr Efficiency, My 15hp is a short shaft version, I do have an 8hp long shaft though so maybe this would be suitable?

Jeff, 5kts, I don't know that I can make that work, even with good seamanship, If I'm going against a 6kt run?
How about if I put a 25 hp on it, would that solve the problem? Or am I completely limited by hull speed?
Thanks for your ideas on shortening and increasing the beam,

Cutting off the point of the bow would be simple, changing the transom angle also easy enough. If I changed it to 90 degrees would that adversely effect the boats performance?

I like your suggestion how to increase beam by putting in a parallel shaped plate in the bottom, maybe a bit awkward trying to fit as it goes into the bow?

 

Ive just watched this on youtube
https://www.youtube.com/watch?v=LMvlmoXaEno

Now I don't know much about sailing boats, but to my untrained eyes this looks like a pretty good boat design.

Opinions please?

 

Either use a wedge shaped insert or just parrallel & accept the flat at the bow, no real issue if the pram bow has a reasonable rake. You might get better than 5knots, maybe ask the Dutch how hard it can be driven, wider at the stern might be good for this too.
Jeff.

 

I'm thinking that this one the Juniorvlet
http://bds.home.xs4all.nl/juniorvlet/juniorvlet.pdf

Might be a better option, it must be pretty stable as it's designed for kids to sail in.
Also size is the length is only 4 meters.

Just increase length by 1 ft, maybe widen by6 "

I'm currently re-typing the instructions for both in Dutch, Google translate doesn't recognise the photo-copied typewriter txt that the plans are written in.
When that's done I can google translate them.

I'm going to start drawing up today to make a scale model