Building Flareline 18, would like to extend by 2 frames...

Bert,

What I and most here are trying to do is get you to look seriously at this issue while suspending preconceived ideas that are preventing your gaining a basic understanding of the problems of changing the scale of a boat. As was said in one of the materials presented to you, changing the scale by any amount does not change all other hull physics by the same amount.

"For example, lets say you want to half the size of your boat, all around. You've found the perfect 30' boat, but want a 15'. Well the law of similitude says you'll decrease it's surface area by 4x (not 2), it's hull volume drops by 8x (not 2) and it's stability dives at a rate of 16x that of the 30' perfect boat. In a nut shell you've made the boat half it's original size, but it weighs 8 times less and is 16 times less stable. Not such a good idea."

This is the critical point you are having trouble with.

Why is a Dutch tank test facility able to do this and not you? Well, along with all other tank modelers over the last 100 years, they have spent man lifetimes, millions of dollars and made many costly mistakes trying to get the scale factors correct. This is very difficult and maybe not any here can actually do it with precision. Only with the advent of sophisticated computer software and expenditure of much more effort have they gotten to the point where they have some confidence in the outcome of such work to risk using the answers to build on without physical confirmation.

Scaling a drawing is not the same thing as adding frames which is what you originally wanted to do.

The reason I have not wanted to feed you numbers is that, unless the reasons are discovered for yourself, they won't mean much. Also South Africa is not a boating wasteland. There are skilled designers there and plenty technology to do anything you may need on this little project.

Where is North Carolina? Well, for a start, it is home to some of the best boating waters on the planet and close to lots of others. Try Google.

 

I'm sorry are you refering to South East Texas?

 

If you build with your intended ideas, without heeding the well schooled advise of others, then it will be clear who the fool is when you launch your creation. No one is insulting you, though your insistence to ignore the wisdom of others, that have way more experience and education then seems that of a fool and is insulting to those attempting to help.

 

Well Tom,

That is the help I been looking forward to . It make sense. If I calculate now the 13% reduction, it means 75,6 % surface area. The hull volume by 43% and the stability is thus non exsisting. ?? I have the following books and shall have to do some homework .
D.R.Derrett - Ship Stability
Lars Larsson and Rolf E.Eliasson - Principles of Yachtdesign
Peter Cook - Boat building methods
Hervey Garrett Smith - Boat Carpentary
Dave Gerr - Propellor Handbook
Roger Marshall -Yacht design details
Arthur Edmunds - Designing power
Glern L.Witt - Boatbuilding with plywood
Glen L Witt - Inboard Motor Installations.

Thank you all for the advice and lessons given. You can understand that I am disappointed.
Rick I still like your design very much, but unfortunately, I have restrictions to 2,5 meter beam and 7 meter in lenght.

Goodbye guys, it was a pleasure to have chatted to you.
Bert

 

It is a pity, I have learned nothing from you. You could have been much more constructive and helpfull. Goodbye Hunter, I am resigning off.

 

I will upset a few people, but I was unable to transfer the picturers into this window. For that reason I attach it as a word attachement.
Bert

Hi Jo, thanks for your e-mail. Sorry to learn you don't have Word on your laptop. For the pictures you have to go to the websites Thanks for your input.
I am going to upset a few people, but I was taken by surprise with my pants down and had not enough knowledge to defend myself or to propose any alterations or alternatives. I did not even know what the transom was. In our language we have different words for all the parts of a boat..

I ordered thus a book from Dokmar.com on stabilities. Also read the book Ship Stability by D.R.Derrett and struggled to revive my higher mathematics. But I got through it.

We have to understand clearly, I bought the plans and paid for it. Not like others who want everything for free.

In my view this boatbuilding industry has a major problem with respect to patent and copyright issues. The copyright has a rule, if an item is changed in 4 dimensions, it is not the same. Thus if I reduce a plan by 8%, all dimensions are changed and it is no longer regarded as copyright infringement. I spoke thus with a patent lawyer and he was surprised that none of the plans I have bought had a remark” Copyright 2007,8,9 2010” etc.also no remark like, Copyright still applicable not withstanding a proportional reduction or enlargement.

Therefore I have to figure out, whether I am taken for a ride to protect this industry or whether it is really true, that, if I change the plan by a small margin, whether the stability is really a very big issue, or an issue which can be overcome. If a design cannot accommodate differentiations of 8 %, I have no faith in the designers of this industry. When I design something, I have up to 100% safety margins build in. Special in crucial area’s

The one thread gave it away. The one from



Building Flareline 18, would like to extend by 2 frames... >>> Thread
Hunter25
Senior Member Join Date: Mar 2006
Rep: 26 Posts: 172
Location: Orlando

The scaling of boats discussed.

constants across boats sizes

Scaling down America Junior plans?




He was too worried that people would copy and scaling down rather high profile designs.




And what about this one..

Boat-building, first-timer design >>>Thread #16 >>>Alan, you scare my customers, don't say that, the truth is never good for business

During the crash course on boatbuilding, I came across some serious issues, like: if I reduce the plan by 13% and overlook that the hull has a 10 meter mast with sail, I cannot just remove the mast + sail and remove the keel, or keels, because the center of gravity , buoyancy will change to a very dangerous position. I will have to work out the righting arms for the new situation.

If I leave the heavy keels or keel on the boat, but only remove the mast, I will not be able to trail the boat, as the gross weight will be way over the limit of the trailer.

If I remove the lead out of the keels, I will probably capsize.

I have thus 3 plans bought, and I compliment the designer on the quality of the plans.

1) The Hartley 28 with a displacement hull.
2) The Flareline 18 with a planning hull
3) The Fisherman 18 with displacement hull for low powered engines

The Flareline 18 is unstable on the sea and I agree with all of you.

The Hartley 28 is an ocean capable boat and require engines > 10 H.P. i.e. > 7,5 Kw
Has all the drawings for the cabin, mast, gadgets, etc in fine details. If I reduce the plans by 8% , (I paid for it) could I compensate for the instability I have created ? That is the big question I have to sort out for myself. The advantage is, I could reduce the mast to 2,2 meters and have an emergency jib sail as standby for the unforeseen moments and could mount the lights to it. The twin keels, I could use to mount the electric motors in.
And if needed, fill them with lead to reach the stability. But I have to calculate the righting arm at 30 degrees heeling and at 45 degrees.


www.hartley-boats.com click on Sail boats – click on Hartley18

If the above mast is reduced from 10 meters to 2 or 2,2 meters, this can be used for a small emergency jib. The roof of the cabin could be used for the 10 m2 solar panels.

Any action has a financial reaction and anything one does, has an advantage and a disadvantage. I will have to judge and find out for myself, whether the disadvantages can be overcome. If you are willing to help me, I greatly accept your inputs. But please , if you are negative, give me the calculations and tangible information. Not just “Don’t Do it” .

The Fisherman 18, I just received yesterday is a low cost, displacement hull for engines > 5 H.P. i.e. > 3,75 Kw But I am not too happy to go onto the sea with this 5,5 meter boat and in my view not “for the eye pleasing” looking high cabin, which looks unstable to me in choppy seas. But I maybe wrong. I will make those calculations also.


www.hartley-boats.com click on Sail boats – click on Fisherman 18


The designer has an original cabin enclosed in the plan,


www.hartley-boats.com click on Sail boats – click on Fisherman 18

Thus I am busy in designing a more suitable cabin, which also can accommodate the solar panels to my satisfaction. Any proposal is appreciated. I myself had something like this in mind:



Original drawing. For 1,2 meter cabin


My proposal with a shaky hand in “Paint” Modified for 1,8/1,4 mtr Cabin -

Bert










Bert

 

I once had the idea to manufacture FG rowboats that were a scaled down battleship .. the "Mighty Mo" .. the Missouri. I decided the only huge problem w this is that the draft would be very small compared to the real thing. That would shorten the WLL, certainly not a deal breaker, but would necessitate a keel of some sort or the rowboat would be blown all over the place. One could say this would be the mother of all scaling jobs .. very extreme but I think it would have worked fairly well. Of course one could give the sides a bit of flare and a few other things but as I recall the length to beam ratio was fine. To say that if you scale a hull 30% it will be a monstrosity issn't accurate but there is a good chance it will be. And Bert if you scale down .. evaluate the scaled boat as if it were not scaled. If you scale a boat down don't say that "oh my god its too tippy" because someone said you loose a bunch of stability w scaling down. Don't even worry about the scale factor (or factors) just evaluate the boat.
One thing I need to say here is that a geographical place called NC to someone in the states (United States) is North Carolina. To someone from South Africa it is nothing. We are an international group w wide spread geography so I think if we give a location it should be information people from around the world can use.

Easy Rider

 

Thank you Easy for your response. I will never go to 30%, at the most 13%, but I have settled for 8%. I firmly believe , and as soon I have calculated all the richting arms at 8% reduction, I will know wether the instability will be of a small or big problem. I do know that the stability could be improved by more SLAB batteries, which implies more power available.
Just lead in the keels, would be a dead extra weight.
Thanks for your input.

Bert

 

Hi Easy, I have finally made my mind up. I drove on Tuesday to Cape Town again and went to see the famous Royal Cape Yacht Club and looked around for the various type of cabins I could use. I came back with quite a number of nice idea's. I have decided to increase the low power displacement hull Fisherman by 5%.

Tom, thank you, because it means that the stability will have improved by 1.05 x 1.05 x 1.05 x 1.05 = 21%
And this 21% stability must be then for the better. One could say, Bert, 5% means nothing, but it does mean the hull by 25cm longer and this is just what I needed for the solar panels. Also I cannot get 8 mm French very light plywood in this country, but only 9 mm. Thus the I will use the 9 mm.

Is everybody now happy? Or is there still somebody out there who says I am a nutcase?

Over the next 36 months I still need your expert input, as I still want to have a small storm jib, a small mast and maybe I will have to consider to copy and amend the lifting keel from the Hartley28 I must calculate the richting arm by various heeling positions for those modifications.

Well I hope everybody is now happy.

Bert

 

By the way, I forgot to ask.

How does one calculate the windforce on a surface area by windforce 5, 6,7,8 ,9 etc. i.e. I have a one square meter area 2 meters from a center pole. What force is placed on the center pole in kgm. What rule of the thumb could one use?
Thanks Bert