Help required on hulls

[Robert Hornby]

I am getting close to commencing work on Columbines hull which will be fibreglass with timber interior and decking. I have sketched up my thoughts on the hull design below the water line but I stress I have no sensible knowledge of this and am requesting some guidance on this aspect. If there is anyone out there who has experience/knowledge of hulls (the prototype was built in 1890) I would be forever grateful.

Robert

[Jayville]

Robert...I can't help but will be following with interest..always wanted to build a small steam launch...please show your progress...clem.   Tasmania

[michaelr]

 Free plans on this site may help you with frame design and give you a idea of what's required for a model steam boat hull.

http://www.john-tom.com/html/SteamPlans.html

Mike.

[Ramon Wilson]

Hi Robert - I would say you will need a bit more in the way of cross sections through the length of the hull for it to be fair. Try Googling - 'Lofting Lines for a boat hull' - Full size or model the principle is the same. Once you have the lines the hull (or form) is relatively straight forward to construct.

Not teaching granny here but are you aware you can build a fibre glass hull on the outside of a form i.e. you do not have to make a mould in order to make a hull - unless of course you want two of them 

Regards - Ramon

 

[steamer]

"From My Old Boatshop" by Weston Farmer would give you a lot of insight.

He always recommended a floatation model....You could do that one half that size in Balsa and test it....in the bathtub....and be pretty confident in what you would end up with...

Farmer describes this procedure in his book.   I used it when I built my boat.    It described it's behavior on the water very accurately!

http://www.modelenginemaker.com/index.php/topic,249.0.html

Dave

[steamer]

http://www.amazon.com/From-old-boat-shop-One-lung/dp/0964120429


You could probably find a copy cheaper if you look local...but that's the book.

Check the library

Dave

[Robert Hornby]

Thank you very much gentlemen for the suggestions and info. I will certainly check out the "From My Old Boatshop" at the library. My real question was more about the general shape of the hull i.e. basically curved as I have drawn it or more of an angular design with chines? I will draw up many more sections when I get the general profile sorted.

Another question for the moderators is where do I post the build log? It doesn't seem like it would  fit into any of the categories.

I am thinking the construction will take a couple of years as for me the best part of model building is in the actual building much more than the finished product. I expect this is true for many of us in this hobby.

I will be making a 'buck' out of high density polystyrene and glassing on top of that, I have a friend who builds model racing yachts using this technique.

Robert

[steamer]

Generally Robert, a length to beam ratio of 5/1 or 6/1 is a good start with a low powered steam boat.   4/1 will work as well.

As a old very experienced boat building once told me.....with small boats...if it looks right...it probably is!

The test tank model built half that size will tell you everything you need to know...on a numeric level...not just opinion.   Check out the book....a good read!    The guy is really funny too!....

Dave

[stevehuckss396]

Another question for the moderators is where do I post the build log? It doesn't seem like it would  fit into any of the categories.

Sure it does. How about the "Vehicles & Models" section.

[Ramon Wilson]

I will be making a 'buck' out of high density polystyrene and glassing on top of that, I have a friend who builds model racing yachts using this technique.

That's exactly what I meant - sounds like you are in good hands 

Sure it does. How about the "Vehicles & Models" section.

Good idea Steve - that's where mine on the 'Wide a Wake' is Robert 

Regards - Ramon

[crueby]

My real question was more about the general shape of the hull i.e. basically curved as I have drawn it or more of an angular design with chines? I will draw up many more sections when I get the general profile sorted.
Robert

Hi Robert, one thing to keep is some flare outwards in the cross section around and above the waterline. It helps the stiffness, as in resistance to rolling, of the hull. Carving from high density foam and glass cloth with epoxy over that is a great way to form up the hull. Just be sure to have insulation around the boiler and engine, since heat over 150f can start softening the epoxy glass layers.

[b.lindsey]

Vehicles & Models works for me Robert. It is a vehicle after all, just goes on water rather than land or rails. I am looking forward to following along.

Bill

[zeeprogrammer]

Vehicles & Models works for me Robert. It is a vehicle after all, just goes on water rather than land or rails. I am looking forward to following along.

 

Excellent. I was hoping it would get posted. Looking forward to it.

[10KPete]

Robert, if you harden up the bilge some and carry that aft and forward it would go a long way to improving initial
stability and give much more volume in the hull for machinery as well as increasing displacement to carry that load.
I think the shear is a bit much also.

Have you looked at any of the steam launch sites yet? Many have lines for these boats.

Pete

[10KPete]

Robert, here is a link to a very good boat designer:

http://store.gartsideboats.com/collections/steam-launches

This page has some nice boats. If you click on a design you can see an enlargement. In the lower left of the enlargement are a
couple of little squares which, when you click on them, will give you an even bigger pic. Take a look at the lines and you can get
a good feel for the classic shapes...

Pete

[Robert Hornby]

Thanks very much for the links guys (especially Pete and Sandy) I can see I wasn't too far away from the basic shape but the linked drawings will help me greatly in getting it just right.
I will be purchasing the polystyrene and fibre glass matting next week from Newcastle (about an hours drive away) and then I expect very much white snow like material on the work shop floor.
Robert

[Bertie_Bassett]

cant help with the design of a hull at all ( in fact probably cant help with much at all) but was wondering how you plan on ensuring the boat sits right in the water once complete and assembled?

to get the hull to sit at the water line I assume you need to work out how much the engine and ancillaries weigh and then compare that to the displacement of the hull design? otherwise she will either sit to high or too low in the water both of which could be potential issues.

also have to bear in mind where about the weight will be sitting otherwise things wont be level?


I might be overthinking things, but i think once i had a rough design i would model it in cad to get its volume (thus displacement) and then do some tweaking where necessary to get things nice and balanced with minimal ballast. 

of course i may well be wrong on all of this, but would hate to build a lovely hull only to find it sinks with the weight of the engine!

[steamer]

cant help with the design of a hull at all ( in fact probably cant help with much at all) but was wondering how you plan on ensuring the boat sits right in the water once complete and assembled?

to get the hull to sit at the water line I assume you need to work out how much the engine and ancillaries weigh and then compare that to the displacement of the hull design? otherwise she will either sit to high or too low in the water both of which could be potential issues.

also have to bear in mind where about the weight will be sitting otherwise things wont be level?


I might be overthinking things, but i think once i had a rough design i would model it in cad to get its volume (thus displacement) and then do some tweaking where necessary to get things nice and balanced with minimal ballast. 

of course i may well be wrong on all of this, but would hate to build a lovely hull only to find it sinks with the weight of the engine!

Bertie......Weston Farmers book will elaborate on how to do all this experimentally, at low cost, and with very good accuracy....Chapter 12.

[steamer]

Robert,

With a hard chine hull, which is essentially a "Sharpie"....you want the chine to enter the  water at 1/3 the hull length, and exit at 2/3 the hull length.

Dave

[Johno]

Hi Robert,

Really looking forward to following your Steam Launch build as it's something I would also love to do given I have a completed Stuart D10 that would come suitable. You may find the this web site of interest; http://mainsteam.co.uk and the associated u-tube videos.

Regards

Ian

[SandCam]

Thanks very much for the links guys (especially Pete and Sandy) I can see I wasn't too far away from the basic shape but the linked drawings will help me greatly in getting it just right.
I will be purchasing the polystyrene and fibre glass matting next week from Newcastle (about an hours drive away) and then I expect very much white snow like material on the work shop floor.
Robert

Hi Robert,

I am pleased the drawings I sent you were of some help.

If you are using Polystyrene foam for your plug then make very sure you get 'Epoxy Laminating Resin' to use with the fibreglass matting.

Polyester resin will dissolve polystyrene foam very rapidly. 

Good luck with the build.

Best regards.

Sandy.

[Robert Hornby]

Rough calculations so far indicate the volume of the hull under the water line is around 25 litres (give or take a few), so if the total weight of the boat is 25 kg then it should sit at the correct depth. The engine /boiler assembly weighs 7.5 kg so I have plenty of capacity in the build weight and should be able to add some extra mass at the appropriate place to get the hull to sit level.
Robert

[Robert Hornby]

I have sketched up some hull profiles, any comments on this?



Robert

[10KPete]

Robert,

Honest comments from my own tastes and experience, OK? Please don't take this otherwise.

Too much shear; looks very toy-like.
Way too deep in the mid sections. It's going to take a lot to push that water.
Way too much reversal between I & J sections, will look very lumpy.
Too much rise in the buttock lines aft.
Some rocker in the keel will give better lines in the dead rise.
Rise should be flatter and the bilge firmer.

Again, just my opinions, nothing else.

Pete

[derekwarner]

Robert.....

1. from your original dimensions we see 1000*330*109 = ~~ 36 litre volume
2. your nominated displacement estimation of ~~ 25 kg would equate to a block coefficient of ~~ 0.75

Considering the fairness of your original sketches would suggest a block coefficient more to be ~~ 0.55 to 0.6
From this and you latter sketch profiles we would expect a displacement nearer ~~20 kg....

A 25% variance in vessel displacement is a large number in hull design considering the fixed values

Derek

[Robert Hornby]

Thank you very much for the inputs.
Pete first. The rise profile is very high on the prototype and the second photo at the start of this post is pretty much full side on and I scaled the deck line from this. I agree it does look a bit ‘toy like’ but then I would like it to be as close as possible to the original.
I do not know how to reduce the depth in the mid-section
The reversal between I and J, I will have a rethink on that one, I agree.
The rise in the aft section is pretty much as the prototype. See photo
I will change the keel to give some rocker.
Derek. Thanks for the calcs, I have reduced the beam a bit to about 190mm from the original 330mm so that will account for some of the volume reduction.



Robert

[derekwarner]

Robert...I am still unsure here

1. from your original dimensions we see 1000*330 beam*109 = ~~ 36 litre volume
2. your nominated displacement estimation of ~~ 25 kg would suggest a block coefficient of ~~ 0.75

3. revising the beam we see 1000*190 beam*109 ~~20 litre volume
4. maintaining your block coefficient [constant here] of 0.75 we see ~~ 15 kg

The confusing point is you nominate the new beam as 'reduced the beam a bit to about 190mm from the original 330mm' , however is shown in the latest plan view as  [2*144] = 288 .....

Derek

[Robert Hornby]

Sorry Derek, Finger trouble I meant to say 290mm not 190mm
Robert

[10KPete]

I must apologise, Robert. I missed the fact that you had a prototype you were working from.

So ignore my comments as I was shaping to a more traditional hull. That said, the picture you just posted shows a very
attractive boat and I think it would make an excellent model!

I'd like to have the full size boat here!

Pete

[Robert Hornby]

Pete I value your input very much, is this a bit closer to what you think might work?

Robert

[10KPete]

Hello Robert,

Thank you for the compliment!

Each of those sections is nice and should work, until you come aft to 'I'. It's way too cheeky to make a smooth transition to 'J' which is very hollow, then the lines come back out to the transom section.

I think what you need to do now is draw the waterlines and buttock lines. Waterlines are the lines parallel to the water and represent
where the water would touch the hull if the water were at that level. The butt lines are longitudinal sections perpendicular to the
waterlines.

You should be able to Google all that up or get a book at the library on boat design.

When all the lines are drawn you will have the ability to 'fair' all of them to make a smooth, nice, hull by adjusting the lines, a
process called 'fairing'. Anyway, it will show up the humps and hollows so they can be smoothed out.

Way more than you probably wanted to know!! It would be impossible for me to give a tutorial on laying down lines so finding a
reference book would be the best way. Is this getting too deep??

Look at the lines drawings in the link I gave you to Paul Gartside for an example.

Pete