Scaling Plans

[sean27]

I am going to be building a Bateau HMD19 http://www.bateau.com/studyplans/HMD...htm?prod=HMD19
I am thinking about scaling the plan up a little. The designer gave the OK for up to 10%. I want to scale it up 8% to keep the beam under 8'6" and length under 20'.

I have paper plans and all measurements are in metric/mm so scaling the meaurements will be very easy to do.

I would like to redraw all the panels at the new scaled up measurements so I will be able to do a nesting plan. I want to find out how much more plywood it would take.

What is the easiest way to go about drawing the new panels? Any suggestions on software to use etc.....

[daiquiri]

Freeship (http://hydronship.net/index.php?lang=en) or Delftship (http://www.delftship.net/) will do the job. Like any software, they have a learning curve - so if you are eager to start buildng your boat as soon as possible, you can ask for help through this forum. There are a lots of experienced Freeship/Delftship users around.
Cheers!

[DCockey]

IF all dimensions are scaled by 8% then the shapes of the panels will not changes. They will be 8% larger in each dimension.

If scaling is done unequally, for example the longitudinal direction (length) is scaled by 8% but transverse (beam) and vertical (depth/height) are not scaled, then the panel shapes will change and simple scaling will not work.

[Ad Hoc]

Originally Posted by sean27

I am thinking about scaling the plan up a little....

Have you factored in the increase in displacement and the increase in power?

For example, at 8% geosim scale, you're going to need an additional 30% increase in power pro-rata.

So that takes the 15Hp quoted up to 20Hp engine.

[sean27]

Originally Posted by DCockey

IF all dimensions are scaled by 8% then the shapes of the panels will not changes. They will be 8% larger in each dimension.

If scaling is done unequally, for example the longitudinal direction (length) is scaled by 8% but transverse (beam) and vertical (depth/height) are not scaled, then the panel shapes will change and simple scaling will not work.

I am going to scale all dimensions, but want to draw out each panel so I can then place them on 4x8 plywood shapes and do a nesting diagram to determine plywood usage.

[sean27]

Originally Posted by Ad Hoc

Have you factored in the increase in displacement and the increase in power?

For example, at 8% geosim scale, you're going to need an additional 30% increase in power pro-rata.

So that takes the 15Hp quoted up to 20Hp engine.

All I did is ask the designer who said 10% max and everything will work out. I don't have the design knowledge to do anything else.

Engine of choice, per the designer, is the 9.9hp High Thrust Yamaha. Should be no problem to use this engine on the upscaled plan since the same engine is used on the designers even larger 24' design. The hull is full displacement so requires very little HP to reach displacement speed.

[Ad Hoc]

The designer should mention to you the increase in drag owing to the scaling, thus the increase in Hp required.

You can use whatever engine you like, just beware you wont get the same performance on the scaled up variant! So if you have selected the 9.9Hp engine this will be under powered by some 30% owing to the 26% increase in displacement.

Originally Posted by sean27

The hull is full displacement so requires very little HP to reach displacement speed.

Be careful with throwing around statements like that, i assume your definition of "displacement speed" is what most amateurs call "hull speed" (which is a gross misnomer to start with). If you say the hull is a displacement hull the opposite is true. If the designer told you this, he doesn't know much about hydrodynamics as the statement is incorrect!

[rberrey]

The design is a displacement hull, even scaled up 8% the 9.9 or a 15hp should be fine. Bateau has a very good support forum that will answer any of these questions you have.Contact cracker larry and he will point you to the right people. Rick

[Angélique]

Originally Posted by Ad Hoc

If the designer told you this, he doesn't know much about hydrodynamics as the statement is incorrect!

Good there is a ‘‘If’’

In another field I have to deal a lot with amateurs, often they don't comprehend enough what you say to give back the meaning of it correct to others. So you can't blame the designer if you haven't heard his own words.

And thanks for all the explaining as I'm the amateur here myself

Cheers,
Angel

[Ad Hoc]

Originally Posted by Angélique

Good there is a ‘‘If’’

And there in lies the problem. "We" never know what has or has not been said and as you rightly point out, how much has or has not been understood and thus communicated to a 3rd party in the manner it was intended.

A "displacement hull" is simply that. It is supported by hydrostatic forces, ie buoyancy. The hull shape makes use of as much buoyancy as possible, for maximum payload whilst at the same time allowing enough "shape" to make the bow fair, to "cut through the waves" rather than bash them and the aft shape suitable for smooth flow into a propeller.

All this leaves is a hull shape that is not designed to go fast for its length and displacement. The faster you go the more power you require. It gets to a point where the amount of power increase outweighs the increase in speed. In other words you can get a suituation where a doubling of power will only marginally increase the speed at best. That is it in a nut shell

[Angélique]

Originally Posted by sean27

Engine of choice, per the designer, is the 9.9hp High Thrust Yamaha. Should be no problem to use this engine on the upscaled plan since the same engine is used on the designers even larger 24' design.

Just checked, the designer said it a bit differently....

Harbor Master Displacement 19' ---> Study Plans ---> ‘‘ Recommended. HP 10-15 ’’

Maia 24' (displacement hull form) ---> Study Plans ---> ‘‘ Recommended. HP 10-25 ’’

There's a lot of good advice here, better learn to take it

Good luck!
Angel

[sean27]

Originally Posted by Ad Hoc

Be careful with throwing around statements like that, i assume your definition of "displacement speed" is what most amateurs call "hull speed" (which is a gross misnomer to start with). If you say the hull is a displacement hull the opposite is true. If the designer told you this, he doesn't know much about hydrodynamics as the statement is incorrect!

This is myself talking. I say full displacement because it isn't a semi displacement type hull.

[sean27]

If you read their forums the designer says that he prefers the high thrust 9.9hp as the best OB for this design. He put the higher HP spec on the study plans to let people know that it was an option if you want to, but says any extra performance in speed will be very, very small with a lot more fuel burned.

My main issue is that I need to learn how to draw out all the panels with the new dimensions in order to do a nesting plan. I will give free ship a try.

Originally Posted by Angélique

Just checked, the designer said it a bit differently....

Harbor Master Displacement 19' ---> Study Plans ---> ‘‘ Recommended. HP 10-15 ’’

Maia 24' (displacement hull form) ---> Study Plans ---> ‘‘ Recommended. HP 10-25 ’’

There's a lot of good advice here, better learn to take it

Good luck!
Angel

[Angélique]

Originally Posted by sean27

My main issue is that I need to learn how to draw out all the panels with the new dimensions in order to do a nesting plan. I will give free ship a try.

OK, back to that

If needed I'm sure you can get a lot help with it here like Daiquiri said in post#2. On the Software forums you might find some answers already. It's also a good place for specific questions about the use of Freeship and Delftship.

Good luck!
Angel

[Chuck Losness]

You really don't need to use software to figure out the nesting on 4x8 sheets of plywood and it will probably be a time consuming adventure. As other posters have said just scale all your dimensions to the new size on a piece of paper for each part. Cut out each part and then start arranging them on 4x8 sheets drawn to the same scale.
When I made my dinghy, I expanded the length by 10%. I drew out the new panel shapes which was simple to do, cut out each piece and then arranged them on the 4x8 sheets drawn to the same scale. It only took an hour or two and I had it all figured out. Your boat being larger with more pieces will take longer but you should still be able to do it in one afternoon or a couple of evenings at the most.
I think that you are over thinking this. Computers aren't always the easiest way to do things. Learning the program will take longer than just doing on with it pencil and paper.
Just my humble opinion. Good luck with your project.
Chuck