Unfortunately due to my double removal in the last 15 months my lab is vanish and I could not manage to build anything including the RG65 with Narrow Deck.
Now, since some time you have instead made some progress and I would like to knows your opinion about the pointing capability of this type of hull.
This was the essential concept of this design.
As explained in the concept description, When tilted, the sides surfaces, once under water, their shall act as a “anti drift surface” and therefore, by principle, producing less lateral drift and and allowing the hull joining the buoy with a closer angle.
To note that the immersed vertical surface is equivalent to about 30% of the fin+rudder surfaces.
Further, when the boat tilt, the projected fin/rudder lateral surfaces are reduced while the hull lateral vertical surface is increasing; a sort of self compensation !
it will out point any boat that I’ve sailed against. but coupled with the speed. on a beat, I can sail underneath a boat and it gives me options to continue sailing and come out the other side with speed. The other option is to begin pointing. and force the other skipper to tack away.
I think if you put a swing rig on it, it would be able to at least point as high as a conventional rigged boat. with the benefit of having a barn door for the down wind run…
I use swing rig, and my experience is different with light winds vs. breeze. Let me elaborate:
Light wind (up to 3kts): the overall width of the hull seems to be a problem. I feel like I got too much wetted area. Pointing angle is not an issue, I can keep up with others, but not at speed. Even if my boat weights 10-20% less than others…
Medium winds (3-8kts): in this range there does not seem to have any difference with other boats, except this specific one that looks faster when pointing (it is a GothMX RG65). My boar points well, runs well, and in general I am competitive.
Heavy winds (8kts+): here my boat has and advantage. When pointing and heeling 40°+, the boat clearly points more than the rest. I was sailing on a pack the other day, and in gusts I was clearly gaining laterally. When running there seems to be no difference with the rest, up to the point where I am overpowered and start nosediving. I haven’t have the chance to test my new C-rig in heavy winds…
If you ask me, I would do the same concept but with a less beam. Like 2-3cm less, so that wetted area is a little less, but keeping the overall shape. Also, remember my hull has a rounded bottom, vs. the flat bottom of your design…
Tarmstro, the performances under low wind conditions are probably related with the Prismatic Coeficient, all other being the same. This is the reason why I drawn lately two RG65 with low and high PC.
See : http://www.rcsailing.net/forum1/attachment.php?attachmentid=14823&d=1410363954.
In the file you may reconize also my last evolution call for a round bottom as you did it.
A narrower hull is part of the potential evolution as some drawings are showing it. The point is that narrow hull means also deeper hull and this is no good either since the wave formation is deeper and producing more drag.
Anyway would be nice to compare ideas !
Thank you again
ClaudioD
tarmstro,
I do have a question about your modification of the hull bottom.
Have you calculated the prismatic coefficient ?
I could do it if you send me the drawing.
For what concern the main section forms, this sketch show possible evolution, but I have some concern about the deepest hull that will generate; deeper wave means also higher drag.
Cheers
ClaudioD
difficult then to establish the volume form of the immersed hull of your model. As rule of thumb I could expect a rather high PC .60 and above.
The Prismatic Coefficient correspond to the ratio of 2 volumes forms : the rectangular box volume with main section constant area containing the hull form volume.
See image from the Larssson & Eliasson book and tipical CofA that I consider the Identity Card of the model. The PC is extracted from the Curve of Area as well the LCB longitudinal position.
Our mono-hull models are ranging between 0.3 to 1.2 relative speed as function of wind strenght. Good average for a speedy model is 0.8/1.2, although 1.2 is probably reached for short time with no waves and breeze …
Took a picture of the shadows used, against a gridded background. I think you may be able to redraw the shadows from it.
Add 3mm all around, as I used these to build the mold using 3mm thick balsa planks. Then I sanded & painted, reducing some… but then again the latex & fiberglass sanwich added some back…
Hi tarmstro,
Before going further I need confirmation of you modification.
I have retraced your shadow profile 4 (3 for the original) and superposed to the original using the deck and LWL line as reference guides.
It appears that your profile is much deeper then the original shadow. In this case is a totally different design and a new calculations are needed to define the caracteristics of your model.
Could you please confirm my assumption obeserving the drawing before I continue for the other shadows ?
Tanks
ClaudioD
Your assumption is correct! I did that! As I said, just aestetics+hunch. As I was cutting the corners, it made sense to me that to keep total displacement the same, I had to increase the height of the hull… Maybe this difference explains the slower speed at light winds?
Anyway… please take a look at the picture. At 973gr total displacement, the bow and stern look a little to low for me… It would be nice if you can confirm this mathematically… Just to be sure drawings/assumptions are correct.
Fine Thomas,
I will try to accommodate your picture with shadows drawings. Of course due to photographic deformation there will be some approximations.
I need to retrace the hull shape as per your shadows as to get a fair form.
The fact that bow and stern are under water is for purpose.
I did it, but with some problems about shadow 4 sizing, nevertheless, with some fairing, I managed to sort out something that could be close to your model! see image.
As expected of course, the static displacement calculations show 1288g therefore much higher then the original Esterel 65 with 1026g.
The model appears to have a draft of 10mm deeper, thus producing deeper wave.
This means that if you say that the model actual weight is around 973g, in this case the boat shall float some 6-7mm higher producing by consequence a shorter LWL. Shorter LWL will produce also lower wet area and less drag.
The Prismatic Coefficient is a bit lower compared to the Esterel 65, suggesting that your model should perform better with medium winds.
Observing the side view it appears that the immersed volume is bit more toward the bow therefore helping against nose down.
This is all I can says, your model is definitively different from Esterel 65.
You may now compare the drawings.
Cheers
Claudio
Added superimposed lines. As can be observed, the major change is the rocker deept changing from 28mm to 38mm justifying the increased hull displacement.
That looks just perfect! Thanks a lot for the work and complete analysis! Simply superb! I now understand better what is happening with my boat, and have you gave me some ideas for a possible future evolution…
Do you prefer I do not call this a “modified Esterel”? I will use some other name for it then…
Hi Thomas,
glad to see that I was rather close to your indications.
the point is that already exist ‘modified’ Esterel-65 called Low PC and High PC, see images, including an RG65 called “n/Arrow” for which I would like to test it since rather narrow but too deep according to my taste : who knows !! I shall wait sometime until my new atelier will be created ex novo in the garage.
You may also distinguish in the image the differences between the low and high PC by observing both the water plan and rocker curve.
Better for you to find another name ! ie: TARM-65
Cheers
ClaudioD
Oh Oh ------ you should never have published the "n"Arrow version of the hull. After hearing about the RG65 Nationals in Florida earlier in February, it sounds like some of the narrower boats were doing well and winning. My building had been confined tot he JIF65 - which is an old design, but perfect for sailors and non-sailors looking for a reasonable boat with hard chines and able to deal with waves.
Maybe I need to look further into your ideas and design. BTW - I "love’ the design name.
Stay well my friend and thanks once again for your wonderful support of this hobby.
Hi Dick,
I was not aware about the Skinny model.
My "n"Arrow-1 has a low PC and therefore expected to be a performer with low wind conditions.
Probably I should make one with higher PC.
Cheers
ClaudioD
watch your email - I’m sending you some photos from the event and some of the “strange” boats - including #181 which is some sort of “Strange” design - Your EsterelE sailed by Marc Smith. Enjoy. Dick
can I get a copy of the 181 photo? never knew any photos existed of the stealth boat…
the wider E definitely needs some extra wind to keep it moving and get on a step…
I will also say having the NCR in the beginning of the year in florida is tough for us Northern Skippers. We have zero stick time going into a big event.
Not that I’m complaining about an exceuse to get to the tropics while we are iced up…
