here here.
My Windy 14 and my Hydra have not had dolphin strikers. It is a pain when righting. The Hydra especially is high sided and no strikers does not make getting back on any easier.
The Windrush front beam extrusio is maybe 6ml thick on the high and low side to compensate.
It is a clean look though.

Interesting comments on dolphin strikers. Anecdotal evidence tells me strikerless is best... The co-owner of my Nacra 6.0 suffered the loss of the dolphin striker, and hence the front beam, due to corrosion in the striker (i.e. where it was drilled for the bolt to connect one end to the beam). On another occaision, I lost a large chunk of flesh from my shin to the same dolphin striker when my helm hurled me forward off the boat as we hit a deep trough while trapezing, with the inevitable result as I swung back in towards the beam (actually quite hilarious, and a source of many a laugh - he refused to slow down while I recovered myself, and more to the point gave me a good tongue lashing for abandoning ship without permission. His face was a picture when he finally saw my leg! Also, as we were in Aruba, plenty of tales abounded about getting out of the water quickly, to escape the sharks attracted by the blood! - and before anyone asks - no, there weren't really sharks - but our wives didn't know that!).

Anyway, by comparison, my Spitfire is strikerless, and has proven itself to be robust and leg friendly. Guess which I prefer!

Do you remember the purchase on the mainsheet system the boom length, hull length and wire thickness that was used on that boat ?

With such data a surprising simple but accurate way of estimating the rig loads exists. It goes something like this, for all you home builders and home modifiers out there.



Pitching moment mast =

(pull in mainsheet line * purchase mainsheet * length boom - righting moment crew+craft * 0.40
+ righting moment crew+craft/0.5*width boat * distance the sidestays are back from the mainbeam

This coveres respectively = moment due to mainsheet - moment due to sail drive + moment due to sidestay (only in centreline plane)

then

Forestay loading = Pitching moment mast / distance bridle points hull to mast step

Side stay loading = Righting moment crew+craft/0.5*width boat

Mast step load = mainsheet pull * purchase + forestay loading + side stay loading + weight rig

Bridle loads = forestay loading ; when the bridle wires are under a 30 degree angle (typical cat rig)

else

Bridle loads = 0.5 * forestay loading * length bridle wires / bridle strop height


Note that the highest stay loadings are achieved not with the crew trapping but with the crew hiking. For a trapezing crew an additional factor (deduction) needs to be added and that lowers the load in the sidestay significant which in turn lowers the forestay load.

Righting moment of a crew hiking can be estimated by :

Weight craft * 0.5 * width craft + crew weight * (width craft + 0.5 mtr)





Example : For a Taipan F16 with a 150 kg hiking crew (no trapezing) and 7:1 mainsheet purchase :


Righting moment hiking crew = 107 * 0.5 * 2.5 + 150 * (2.5 + 0.5) = 584 kgm

Pitching moment mast = 50 kg * 7 * 2.15 - 584 * 0.40 + 584/1.25 * 0.70 = 846 kgm

Forestay loading = 846 / 1.37 = 618 kg

Sidestay loading (hiking crew) = 584/1.25 = 467 kg

Mast step load = 50 * 7 + 618 + 467 + 25 = 1460 kg

Bridle loads = 0.5 * 618 * 1.22 / 0.7 = 539 kg (my Taiphoon has a larger bridle angle of 35 degrees)

This means that if all sailing conditions are perfectly stable (no dynamic forces c.q. gusts, shock loads, crew moving aroun) that the force situation needed to just keep the mast motionless on the vertical REQUIRES the above loadings. Without them the mast will fall down. Of course, dynamic forces will both increase and decrease the above loadings. A typical safety margin is to choose wires that can withstand 150% to 200% of the above calculated loadings.

The accuracy of the above numbers is around 5% from the modelling perspective. I've neglected the angles the stays make relative to the vertical and the pressure on the boom. These are however very small contribution. An example, A boom loading of 100 kg will only increase the mast step load by a mere 3.4 kg (=0.23%)!

I made a excel sheet with a more complex model then above and the results there don't differ by more then 5%. Making a similar model in some fancy designers software isn't going to produce more accurate results. Mostly because the same assumptions need to be made anyway and these are most limiting on the accuracy achieved.


Now all you homebuilders can design your own rigging.

Wouter

Ahhh, a dolphinstrikerless setup can be made to work, some of the earlier Stealths had these as well.

The downsides are :

- A heavier boat (by about 5 kg at least, most often by a shy 10 kg)
- Trouble keeping the mainsail leech tight (even with a much heavier beam)

The above two reasons are the causes why any formula based racing boat has a dolphin striker setup or (dolphinstrikerless) carbon beams. However, there are also a good number of examples were carbon beams are also fitted with a dolphinstriker setup for additional stiffness.

These issues became increasingly more important when the craft becomes wider. A dolphinstriker setup scale well to a wider width, a dolphinstrikerless setup doesn't. The latter means that the beams must become disproportionally heavier to maintain the same overall stiffness under mast step load.

I think the Spitfire is the only wide design with a dolphinstrikerless aluminium beam setup. All others are more narrow or use specially reinforced carbon beams.

Wouter

Thank You.

Easy to understand (for the most part).

This aprox 100 strands of Aramid (Kevlar) holding 217 kgs.

Dind't look like breaking. Just tied knots in each end (they slipped), no protection from fraying.

Further experiments are iminent, along with some specs.

TJ

Thank You

Easy to understand. (for the most part)

TJ

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