Most recent posts shown first (Show Oldest First)  (Print Booklet) 
๐ฌ Re: COORDINATES
14 days ago by ๐ฎ๐น AlessandroSPQR ( Vice Admiral)
โง 17 Views ยท 1 Like
Flag
Sorry Ross, I only replied to the private message now. I read it some time ago, with the intention of replying as soon as possible and then I forgot.
In my haste I may have made some mistakes, bear with me. ▲
โฉโฉ
Len1

Login To
Remove Ads ๐ฌ Re: COORDINATES
28 days ago by ๐ฎ๐น AlessandroSPQR ( Vice Admiral)
โง 25 Views ยท 1 Like
Flag
Hi Ross, sorry for the delay in replying to your PM, check your private messages folder now.
▲
โฉโฉ
Len1

๐ฌ Re: COORDINATES
30 days ago by ๐จ๐ฆ RossM ( Lieutenant Commander)
โง 26 Views ยท 2 Likes
Flag
the last with mathematics was a beginner calculus in 1974. They gave me a PASS if I promised not to come back.
▲
โฉโฉ
Len1
AlessandroSPQR

๐ฌ Re: COORDINATES
30 days ago by ๐ฌ๐ง luckyduck ( SubLieutenant)
โง 28 Views ยท 2 Likes
Flag
Ross, you must have the pattience of a saint to work all that out, plus a degree in mathematics and Excel๐ค๐ค๐ค
▲
โฉโฉ
Len1
AlessandroSPQR

๐ฌ Re: sailing
1 month ago by ๐จ๐ฆ RossM ( Lieutenant Commander)
โง 39 Views ยท 2 Likes
Flag
CE:LCP schooner is truthfully a range 712% (I am aiming for 7 and hoping for 12)
▲
โฉโฉ
AlessandroSPQR
Len1

๐ฌ Re: sailing
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 46 Views ยท 3 Likes
Flag
Hi Ross agree entirely! The 4% I quoted is for the yacht illustrated it has also worked for a standard Bermuda rig.
I have a schooner on the back burner and thanks for your info advising 7 % I will take note of that and apply. Always learning! I love it! Best Roy ▲
โฉโฉ
AlessandroSPQR
Len1
hermank

๐ฌ Re: cartesian coordinates
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 47 Views ยท 1 Like
Flag
Hi all, nice to do the maths but which is most important, the calculation and solution or constructing a practical model?
When scaling down from a prototype as we know, hulls and sails do not change in proportion to each other. I start from the size of the finished model, i.e. will it fit in my car and also have a place in the house. So working out a suitable hull size comes first. Dividing the model length into the prototype length gives a scale. The cube of the scale gives a 'scale displacement', in some scales just not practical! All my models have to earn their living at the lakeside. It is fortunate that to make a model sail, the invisible part under the water can be doctored in many ways. The models by Glynn Guest have relatively crude hulls and what used to be called 'stand off scale' appearance. I have built several and they look good on the water. I also enjoyed the construction. So we have to decide where your interest lies? Doing exact calculations for hull displacement is conditioned by sailing in water (and waves) that have obstinately remained at full size. Hull displacement calculations could have a 10% error but it would not be noticeable when on the water. Bearing in mind that all the mentioned calculations have an end in practical sailing. If only constructing a display model the numbers are irrelevant! It reminds me of the radio control of the 1950s where the boat was the least important aspect of the model! Just my two pennorth! Roy ▲
โฉโฉ
AlessandroSPQR

๐ฌ Re: block coefficient
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 53 Views ยท 3 Likes
Flag
If you look at the hull lines, draw the limiting line under the hull before it drops at right angles to the keel. Everything above is the hull to use in calculations.
The keel is then measured almost as a trapezium in crosssection by the area. With a hull built and ready to float and weighted correctly fore and aft. I put the hull into a bath full of water. I do not make big ones any more! I have already put some cheap masking tape around the middle and side of the hull. With a pencil I push the hull sideways through the water. Find the sweet spot where the hull moves evenly, not going to one side or the other, and mark it. This is the CLR. When the sail area calculations are done and the C of E of the sail area is worked out, it is this point that should be placed 4% ahead of the waterline length. This will give a nicely balanced sailing attitude. The mast can then be mounted in the position already determined by where the C of E is to be. I do all this before working out where access and s/s should be. By this I mean with sails at 30 degrees she will sail a straight course with no rudder adjustment needed. My last 3 yachts have been set up in this way and they work fine. With Bella there was a set mast position on the plans, I ignored this and moved the mast position back aft 2cms, which was as far as I could. To get a better balance, i installed a bowsprit and the fore jib is moved forward until the C of E is just ahead of the CLR by 4%. The length of the bowsprit was now determined. Fittings were soldered up and she looks just right as well! The fore jib is on a loop and fixed, but after a year sailing her I decided to have a standard servo with a small arm fitted to pull in the fore jib sheet and tighten sail. The effect is dramatic! Careful control creates a wind slot for the jib and main sail and she speeds up. Roy ▲
โฉโฉ
AlessandroSPQR
hermank
RossM

Login To
Remove Ads ๐ฌ Re: block coefficient
1 month ago by ๐จ๐ฆ RossM ( Lieutenant Commander)
โง 48 Views ยท 2 Likes
Flag

๐ฌ Re: block coefficient
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 55 Views ยท 1 Like
Flag
I don't think the extended keel is taken in to account in the calculation. The numbers I see are 0,45  0.55 for sailing yachts.
When I modified the Aeronaut Bella yacht I beefed up the keel with 3mm bass wood each side as I did not think a 3mm keel could support a 1 Kgrm lead weight. It was given an aerofoil finish and the 2 keel weights were screwed back in place. I worked out the additional buoyancy from the keel which by chance equalled the filled in lead between the keel pieces. The waterline stayed exactly the same and the righting moment had improved. With the gaff rigged sail suite I drew up and made, there was a 40% increase in sail area but the C of E had dropped much lower so she sails very nicely. I am still trying to find someone with a standard Bella with the Bermuda sails to compare. Roy ▲
โฉโฉ
Len1

๐ฌ Re: RR or RR
1 month ago by ๐จ๐ฆ RossM ( Lieutenant Commander)
โง 53 Views ยท 1 Like
Flag
I lean more to de Cervantes than to Shakespeare
▲
โฉโฉ
Len1

๐ฌ Re: displacement
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 59 Views ยท 2 Likes
Flag
Remembering back too many years I recall multiplying frame areas 1424241 and doing things to them I have forgotten.
On another point of kit production by Deans. Ron told me that they obtained permission to produce models from original plans by Camper and Nicholson. We had a couple of motor yachts, Melita and Dufresne and the very large yacht Blue Leopard. The proviso was that he could use only the prototype drawings and not adjust them for a model. I talked to Ron when Blue Leopard was first put on the market. He challenged me to find out what he had done. As I knew what to look for I saw he had made the keel very wide to gain more displacement. I was hoping to have the model to do a build review for the International Boat modeller magazine. The then editor was also a yachtsman and did not like the way it was set up as a model and said he did not want it reviewed. I was a bit 'iffy' about it as well so there we are. If anyone is interested the original Blue Leopard model yacht, which when viewed, does look good on the water is now on sale. I have sailed this one as Ron let me take her out for a spin at the late Pangbourne model boat show now defunct and she does sail well. Roy ▲
โฉโฉ
Len1
RossM

๐ฌ Re: displacement
1 month ago by ๐ฎ๐น AlessandroSPQR ( Vice Admiral)
โง 59 Views ยท 2 Likes
Flag
Good evening to all naval modelers.
I mainly answer to the double R: Roy and Ross, but this message is for all modelers interested in this topic. I thank Ross for reopening it. Actually, let me say one thing: I really like it, in fact I adore "much ado about nothing". I already said that for those who design a hull for a sailboat from scratch, knowing certain information is important, in fact essential. But here we talk about it for pure pleasure and I like to hear your ideas, especially from people so prepared and sharp. Tonight I really got behind with the messages, there is a lot of meat and cooking and I hope I understood everything you said. I will reread it better even after this message. So I start from Roy's message in this topic that begins like this: "Have you tried the old methods? I get a good estimate using the Prismatic coefficient..." And I will follow the discussion in chronological order. I speak as a layman and ignorant compared to you but the prismatic coefficient method, although valid, is not the most precise, in my opinion. It is certainly the fastest. If you remember, in the topic (see link at the end) of the Esso Deutchland tanker by JockScott (hey Jock, greetings from me, you see that your question was very interesting) we had addressed this issue. More precisely in message no. 33 of that topic, dating back to about nine months ago, I had compared the final results of three methods to calculate the immersed volume. The methods were the following:  3d software method.  mathematical/geometric method (without 3d software).  prismatic coefficient method. The most precise value is the one provided by the software. However, you need to have the software and you need to know how to use it. The prismatic coefficient method is fast but the least precise. The method I called "mathematical/geometric" is very laborious and long, but precise and does not require software. I will not repeat it here (I described it in the second attached link). I have not read it anywhere, it seemed the most logical and natural to me, especially when I learned to draw (badly and little unfortunately) with Rhinoceros. Of course I have not invented anything new and who knows how long it has been used. I simply want to say that (for having arrived at it by myself) it is quite simple and intuitive. Before moving on, a question please: in point no. 1, where you write: 1 Measure area of โโ2 adjacent stations. Are you referring to submerged sections? In that case, how do you calculate the areas of sections with curved lines (that are not circles, ellipses, parabolas, hyperbolas etc. etc. i.e. not identifiable by a mathematical formula or function)? Do you use the method I used for JockScott? The method that Ross intends to follow, instead, seems different from all the three listed. I think I understood it from these sentences of yours: "This isn't the usual 'measure the area of โโthe crosssections and multiply by the length' I did that in high school, and it worked well. I want to try something different this time. This is not my tested and proven method yet. It is still being developed." Probably the method you discarded is, with some small variations, the one I prefer and use (in the absence of software). Well, this intrigues me a lot. I am absolutely curious to see it. It doesn't matter if it won't be a sure success, the mere fact of trying is a merit from my point of view, you have all my moral support. Well, now let's get to your method. I think you explained it from the point where you start with this sentence: "So, visualize an imaginary box that the vessel ..." I have to be honest. I need to reread it a few times and maybe I'll ask you more questions to understand better, (sorry but translations always put me in difficulty) but like this, at first glance, it seems to me a compendium between the calculation method that Jock Scott empirically did and infinitesimal calculus (but very empiricalpractical and without formulas). If I understood correctly, this method becomes more precise the more cubes of subdivision there are. That is, if instead of 28 units you use many more (increasing the subdivision) you increase the precision. However, whether I understood or not, it is truly a method that interests me a lot, logical and not impossible to apply in practice. You have my full attention. I will follow all the developments. Finally, I take a small step back to your question: "Question I ask here, are there techniques that will allow paper drawn curves to be transferred to computer hull design programs? " I don't know if I have understood your doubt perfectly but I can tell you that if I have a drawing done on paper, after having scanned it, I have no problem with Rhinoceros to trace all the lines (frames, keel, water lines etc. etc.) in order to reproduce the drawing on Rhino. Creating the hull surface and the volumes is much more difficult (at least for me, not for the good ones). I already did it for the JockScott tanker. So if I understood the question correctly, the answer is: Yes, it can be done. However, if I understood the question correctly, if my answer is correct, your method continues to interest me a lot. ▲
โฉโฉ
Len1
JockScott

๐ฌ Re: displacement
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 62 Views ยท 5 Likes
Flag
I started learning the basics from an EUP notebook size book called 'Teach yourself Naval Architecture'
I got halfway! Roy ▲
โฉโฉ
xtramaths
Len1
AlessandroSPQR
RossM
hermank

๐ฌ Re: displacement calculations
1 month ago by ๐ฌ๐ง roycv ( Vice Admiral)
โง 64 Views ยท 3 Likes
Flag
Have you tried the old methods? I get a good estimate using the Prismatic coefficient.
This takes the immersed centre area bulkhead area multiply by the length at the waterline and apply the coefficient for that type of hull which will be a decimal value. Yachts are around 0.45  0.55 ranging to bulk carriers at 0.95. A solid block would be 1.0. Another way for similar ended hulls is to treat the ends as half each so two ends = 1 and then calculate the centre portion. The first programme I ever wrote was to produce a lookup fanfold printout to do just this. That would be in 1966 and written in PLAN. I hate programming! It can take you over thinking about it. I leave it all to my son. ▲
โฉโฉ
AlessandroSPQR
hermank
Len1
