Originally Posted by Tom Corbett

. . . The finish places should not be read as indicative of anything . . .

Thanks for the complement Roy. You’re so sweet. But you hit the nail on the head about the fun part. When you get a puff with all that horse power, that Viper M boat would jump out of the water and take off. Big advantage with that 17 inch fin too. Not only the low wetted surface, but I had 2 meters more of shoreline to play with on the far shore starboard tack lift typical on the Mission Bay pond. And that Kevlar hull without a lick of paint was easily the lightest boat there. To top it off I had those gandfathered big roach sails on a Bob Sterne A+ rig. Maybe 2nd place doesn’t mean much to you Roy, but whooping Gary with his brand spanking new fangled machine that was proofed at the Worlds was OK by me.

Mostly braggin'; not phishin'. JWB

Nice.
Moving right along now that the clarification has been clarified.
Thought Id mention I sailed a slow M today. Still fooling with the telemetry, but 3.7nm travelled and 5.59 knts. Not bad for February.

about weights, see #2665
nowadays, the total weight is in the order of 4.8 to say 5.5 kg. Note that the fin length is close to the maximum. It seems that using the maximum length is not so benificial, so it is about 50-55 cm from hull bottom to top of the bulb

It is interesting to see the advantage of less draft when the bottom slopes up near the shore!

Originally Posted by Joost vs

about weights, see #2665
nowadays, the total weight is in the order of 4.8 to say 5.5 kg. Note that the fin length is close to the maximum. It seems that using the maximum length is not so benificial, so it is about 50-55 cm from hull bottom to top of the bulb

It is interesting to see the advantage of less draft when the bottom slopes up near the shore!

Thanks for the info. I have a design for an M that I'm toying with. I doubt I'll ever build it but who knows?

Have you have some details? Having designed several, I may be of assistance.
Joost

This is what I have so far. Currently she displaces 4700g and I need to increase that to closer to 5kg. This is a stretched RR II.

Can't upload .gpx. Sry! Nevermind.

Still wrestling it a bit, but here are some telemetry logs from a Marblehead.
Just having fun, not under sooper cerious racing conditions.

With Swing Rig:
https://connect.garmin.com/modern/activity/1597031277

Conventional A-Rig:
https://connect.garmin.com/modern/activity/1597035978

Must be those downhill runs giving the speed! (11 ft & 8 ft)

Last Sunday at Mission Ridge I only managed 52.4 mph. The snow was fast but to soft for real speed runs. Two weeks ago I got 54.6 mph and last year I got 55.4 mph. The effects of speed on skis is so exponential it's mind boggling.

Originally Posted by davidjensen

This is what I have so far. Currently she displaces 4700g and I need to increase that to closer to 5kg. This is a stretched RR II.

1
Unfortunately, being dutch, I do not know what an RR is?
2-2
Your lines look very nice, using round sections helps to reduce the wetted surface which contributes more to the resistance than for large yachts.
2-3
not going to the full waterline length (overhangs fore and aft) also help to reduce the wetted surface, though this is only in light air
3
the loss in stability having a small beam can be counteracted bij having a fin length which is close to the maximum , see the rules
4 -1
note that the maximum allowed length is 1290 mm, not 1280 as suggested on your drawing
4-2
I'm not fully convinced about using a knuckle
4-3
you have a large freeboard forward but not so much aft. If you heel your design up to say 35 degrees, does the deck aft stay dry ?
4-4
what is the prismatic coefficient beingvolume divided by (lwl* main section area). Should be in the order of 0.56
4-5 where is the LCB ?
5
the bulb volume is given by 205 cc resulting isn a dry weight of 2.316 kg which, as I see it, far too low unless you aim at a light wheather yacht
usually the weight is in the range of 3.2-3.6 kg
6
keel or vin volume looks OK. Note that a thickness of about 6-7 % of the chord is the way to go. Difficult to achieve such a thin fin with sufficient stiffnes. Carbon to the rescue.
7
Did you look at the separate components of your weight ?
on
http://www.modelbouwforum.nl/threads...237053/page-16
you will find "my" weights, look at entry #301.

Also, check the longitudinal centre of gravity.

for more technical information, look at Fossati:Aero-hydrodynamics and the Performance of Sailing Yachts
for general information, Graham Bantock provides a whealth of information at sailsetc2.com
success!
joost

Originally Posted by davidjensen

This is what I have so far. Currently she displaces 4700g and I need to increase that to closer to 5kg. This is a stretched RR II.

Hi David, Nice first up design.

A few things that may help:
- Current leading designs are around 4700 - 4800g. Hull weights with everything in ready to sail (less rig and fin/bulb) should be under a max of 900g. Current leading boats around 750-850g
- rig weights are around 300g for a conventional A rig and approx 275g for a light swing A
- bulb weights are between 3300 and 3400g
- fin depths are short of maximum
- the leading setups have swing rig for A rig and conventional shroudless rigs for lower. Swing rigs set high on a foredeck are a complete no-no and slow so you may like to give consideration to a flush deck with a taller stem for shedding water downwind.

I would be happy to offer some numbers relative to your hull design and balance if they would help.

Cheers
Brad

Originally Posted by bbbp

Must be those downhill runs giving the speed! (11 ft & 8 ft)

Like I said, still wrestling it a bit, but Fairly certain boats go downhill when you put them in. Peticularly when water level is ~2 feet below the standing grade

Joost Thanks for the info. RR stands for Race Ready which is the name of my current design and build of which you can find my build log here.

https://www.rcgroups.com/forums/show...e-a-d-y-II-IOM

Thanks for the offer Brad and I may take you up on it later on in the design. I need to look at more pics of the current designs to get a better idea of the above water line designs.

This Marblehead design is a stretch of the IOM design. Right now I am just dealing with everything below the decks and can adjust the freeboard and how the nose and foredeck work with the rigs etc. I am under the assumption that you can build a rig very similar to an IOM rig for the M. Another question I have is about the rule dealing with the keel and its 0.6" deviation from the fore aft center line of the hull. Does this mean the leading edge of the keel can be no more than .6" behind the centerline?

Originally Posted by breakwater

Like I said, still wrestling it a bit, but Fairly certain boats go downhill when you put them in. Peticularly when water level is ~2 feet below the standing grade

In reality, most consumer GPS units will show an elevation change just sitting there, or moved about without an elevation change. THe WAAS enabled ones will stabilize out after a few minutes at a fixed location. My best hand held missed its known location by 5 ft HZ and 6 ft vertical, compared to our survey grade units. Plenty close to find something!

BP