Originally Posted by BiggsDarkLighter

BTW Earl, did Steve Crowes ever find out anything more past his article you posted up?

And, do you happen to have more pictures of the "original Dawn" as hinted at by that article?!

Sorry, no, that's all I know about the boat.

Cheers,

Earl

Searching on the Web I found this : https://www.rcmodelyachts.com/2017/1...cted-boat.html
A sail plan is drawn for the Marblehead, can someone confirm ?
In this case the RM calculations published at post 58 are false !
The results shall be much better

That is Steve's (SeattleRCSailor) Wampum build. He is watching this (and has been working on files for it too actually) but I will bump him a pm!

He did an AMAZING job on his builds!

But, if you look back at one of the original line drawings, you will see it was running a high aspect sailplan to keep away from the vane feather. It's sailplan looks a LOT like a modern Marblehead one.

Just triangles, taller mast may be ...

When analyzing the older free-sailing boats it is important to understand just how lightly built they were and the corresponding ballast ratios they achieved. Rip Tide, as designed, had a 73% ballast ratio. Ted Houk's son told me his father, using George Pocock's cold molded techniques, beat that ratio in the actual boat.

Cheers,

Earl

Originally Posted by ClaudioD

Searching on the Web I found this : https://www.rcmodelyachts.com/2017/1...cted-boat.html
A sail plan is drawn for the Marblehead, can someone confirm ?
In this case the RM calculations published at post 58 are false !
The results shall be much better

Hi Claudio. You found one of my posts on my blog. The images are of the Wampum 2, an M from 1933. The image is supposed to be the original sailplan and was sent to my by Earl.

Claudio, those sail lines you just posted above actualy look pretty good!

Earl, well from what I have seen digging through my book pile is the winning build thought for vintage, yet simple, seems to be a thin oak former or brace rib steamed around the shadows. Easy enough, and I can try a new woodworking technique in the process. Then, use stringer triangles to transfer the weigh in key places like chainplates.

That with basically no shadows left in the boat, and decently thin planking should get us a solid and light hull. I do not plan on glassing the outside, but may use thinned resin. Finishing will be sorted out a bit later.

But still keeping in mind that we went from the 62" down to the 50" hull, do we need to bump depth up 10% and beam up 5% or something like that to get back some displacement?

5% all around looks best. 10% and 5% looks okay. Playing with numbers to see if something in the middle looks better.

Okay some imagination will have to be used. Shadows are not corrected in both directions, only the vertical. I did not cut pics apart and scale height and beam separately either like would be needed.. So kinda have to mix and match upper/lowers (height/sideview, beam/topview) to get the idea.

Or if nobody thinks it is going to be a problem, just build with no additional added back in? Reminder, 62.25 to 50 is a 20% decrease.

I can (pretty) easily scale the lines this way, and I suspect the same could be done on lines in 3d format too? Or hopefully any other 2d file made up.

EDIT: The way the files upload, it looks like the hull length is increasing when you scroll through them.

Hope not confusing your mind with my BlaBla, I do not knows if the DAWN is already a reduced scale from a real one.

When I decided to build the TUIGA, see attachment , a 15mt SI , I considered various scales and find out that below a certain size limit it become very difficult to build the model.
This is mainly due to the scale factors that influence dramatically the weight simply because of the "cube factor". When you say that the difference 62"-50" is only 20% in length it is not the same for the volume that obey to the "cube".
Let check :
If the 62" has a displacement of 23lbs, what will be the displacement of the 50" ?
According to the scale 62/50 = 1.21
The "cube" will be : 1.21x1.21x1.21 = 1.77

therefore 23lbs divided by 1.77 you get the new displacement for the 50" model that is : 23/1.77 = 12.9lbs

As you can see the 20% length difference produce almost the 50% in Volume.

The difficulty start when it is decided, for stability reason, to allocate 65-70% of the 50" model, the ballast volume will be : 12.9 lbs x 65% = 8.38 lbs and more if 70% is retained and less left for the construction.
12.9 lbs - 8.38 = 4.52 lbs available for the full model construction !!! This is where the problem start ...

Modifying the hull/keel shape will disturb the lines and very probably the sailing performances including the Righting Moment versus Wind Speed.

Back to the 62" model the ballast will be : 23 lbs x 65% = 14.95 lbs and 23 - 14.95 = 8.05 lbs for the construction almost the double compared to the 50" model

No need to modify the hull /keel lines of the 62" model, but of course the model will be larger and introducing other factors like the transport, etc..

At the end, you have a choice, with the 50" model you meet the VM Class requirement but need to accept to reduce Sail Area when the Wind start blowing over 6/7 kt or have more wind performance with the 62" and adds transport problems and change Vintage category.

Modify the keel means loss of Sailing performances due to increased wet area and drag , better RM and increase construction margin , but this late need verification. IMO will be easier to change the RIG and keep the design lines as they are !

RC Sail models are always a matter of compromise !

Up to you !

Hi Claudio,

Based on the plans shown back in one of the early posts on this thread, the Dawn was designed as a MODEL, not a full-sized boat. It was an A Class boat. Given that, then we probably don't need to adjust anything for the A Class sized model, and may only need to slightly fiddle with things if we scale it down to a 50" Marblehead size.

I really think that we're overthinking this. I'm going with a straight 50" version of the original Dawn with only a slight increase in the 'relative' size of the ballast.

Steve

Steve, a 5-7.5% side/depth increase and a 5% top/beam increase is easy enough, is it worth it? It does slightly alter the lines but not enough to tell without the original next to it.

Thank you Steve,
no problem then with the 62" model as being the original design where Displacement , Ballast and Sail Area were studied, instead the down scale to 50" is introducing the typical scale problems with particular influence to the Righting Moment.
Keel modifications need to be analyzed with calculations.
Increasing ballast requires increase of buoyancy as well

Claudio

I went back to previous Static RM calculations by using the drawn Sail Plan of 793in² published before and check with various Wind Speeds .
The remarked improvement from 5kt to 7.5kt is derived by the CE lowering of the rough sail plan .
No much left for the construction 2.5lbs (1.13kg) if 65% ratio is keept.

Claudio, does my proposal to add back a 5-7.5% (or even 10% if really needed but prefer to stay at 7.5% max) side/depth increase and a 5% top/beam increase give us enough room to make it worth doing???

I have no idea how hard it is to multiply existing bits by these numbers and recalculate this...

I fiddled with some dirty calculations (again no real idea how to do them but guesstimated using percentages) and it seems to me that if we can get the displacement up to something between 12.8 and 13lbs with this alteration. Or 5.81kg. This gives us ballast of 3.77 or 8.31 lbs. SO this would take the space for the hull up to 2.04kg or 4.49lbs.

My math again is super dirty and sketchy though. I basically just averaged the two dimensions and assumed a 6% volume increase... 4.49 lbs still doesn't seem like a lot of space left to work with, but much better than 2.5lbs.

Plus, that calculation still drops the heel 7.5% and that isn't accounted for in bettering the RM.

If somebody can fix my calculations and redo the other math.... Would be nice to figure out if that small alteration puts us comfortably back into a safe zone.

Again, guesstimate and I am likely not doing the math right. but I suspect I am erring on the side of caution

I posted a question a ways back that got lost in the confusion.

Can somebody explain the lines issue? I couldn't see where the original plans are messed up and lines weren't matching/working. Again, I was simply using calipers to compare measurements though.

Next, if I were to use the original shadows and sideview, planking etc, would that get me "this" boat? I am guessing the "bad" lines are the horizontal buttock(?) lines (I think that is what they are called)? If so, how much do those really matter if I am fairing from the shadows and keel profile?

This is where not understanding and getting my hands dirty with the 3D CAD stuff puts me at a disadvantage.

BDL,

The lines on the original plans for almost all boats drawn in 2D don't match exactly due to a number of factors, including; The degree of accuracy needed, the issues with scanning paper, and the perhaps the biggest issue is that they are simply drawn in 2D.

When creating in 3D, you are building ONE thing, and you can easily see where things don't line up, as opposed to drawing a profile (side or elevation view) in 2d, and then trying to take measurements off of that drawing to hand-draw a separate sections view and then another separate plan (deck) view. Even if you're drawing in 1:1 scale for a model boat, it is pretty much impossible to accurately measure one line and then accurately transfer that to another drawing in a different view. And I'm only talking about the three views mentioned. I don't even use the buttocks or the diagonals. Remember that the 2D designer is making SEPARATE drawings. In 3D you're making ONE model.

Let me try that a second way: In 2D, with separately drawn views, if you on the computer made an EXACT copy of the sections (half-section actually) and rotated it and tried to fit it onto the profile (side) view, it would probably not fit when you get down to the thousandths of a mm. That's just not good enough. In 3D, surfaces and solids don't work unless things fit EXACTLY. So, when modeling in 3D, that's what you have to do... you have to make the lines fit exactly, and when you do you get a surface or a solid. You know when you get it to work. So we adjust the 2D drawings to work in the much more accurate 3D world. From that, you can make laser cut pieces that you know will fit.

So I start by tracing the sections and the profile, and then try to match them up and get them all aligned. I usually have to add a deck line and then scale each section a bit to match the profile and deck-profile lines. But when done, you end up with a model that is much more accurate than virtually any 2d drawing... even ones that are drawn on a computer. I've tried to convert a few 2D AutoCad drawings of boats to 3D... you'd think it would be easy... but even those are usually off by a bit (lines don't connect, sections aren't accurate, lines aren't completed, etc...).

By the way, I'm tinkering each day on a frame or two for Dawn. It'll still be a long time before I'm done as I'm simultaneously tinkering on several other projects! But here's how it looks as of tonight:



First four frames done. The alignment jig is being developed as I make the frames. The keel is roughed out but will need to be tweaked as I do the center frames. I'm using the same keel system that I used on the Wampum 2, so the two-part ballast will be fixed (very permanently) to each side instead of one ballast hanging from screws.

Steve