I occasionally come across shortish reduced diameter masts at attractive prices.

Is the diameter of RDM masts small enough to pass through the ferrel of an SDM mast & therefore be used as a mast stiffener?

Jim Michaels

Hello Jim, hope you got some sailing in this season.

RDM masts are generally used by the wave sailing guys because they are very durable. They tend to not be as stiff as SDM so also tend to be used only in the smaller size sails.

An RDM would probably be too much of a noodle to use as the main mast for the larger size sails we normally use ice boating but I would think a RDM stiffener would work just fine in a SDM mast as long as the stiffener was long enough to fully contact the ferrule (assuming your main mast is two piece) and extend at least significantly to the bottom of the mast. The smaller diameter shouldnt matter (at least I dont "think" it will matter..)

My local ice (the South Shrewsbury River) wasn't thick enough this year to support a goose. I hope to drive the 6+ hours to N.H. midweek to take advantage of the forecasted overnite freezes. This assumes that the ice will last 'till then. I'm curious how my new on-the-fly outhaul tensioner works under real loads.

My thought with a complete RDM as a stiffener inside an SDM mast was to maintain a constant curve under load. My impression is that use of mast tops alone simply protects the bottom of the mast. Of course, having the top easily spilling wind might be a good thing that delivers more overall benefits than maximized thrust. I yield to everyone elses experiences on this subject.

Jim Michaels

Jim, Ive never stiffened a whole mast so dont know what will happen but now that you bring it up, stiffening a SDM (standard "larger" diameter) mast with a RDM (reduced "smaller" diameter) mast might be interesting. The SDM mast would probably have to be one peice because it would have no ferrule to get in the way and the RDM mast more than likely would only make it up about 2/3 of the way up the total mast but that might be enough to make a difference. The original "need" for stiffening was both for strenght and performance and you will get a benifit in both areas.

Regarding the twist on windsurfing sails, I agree they probably have too much for ice boating applications but Im not sure that the twist is really much of a problem as it doesnt really seem to slow the sails down that much - if at all. The most noticable thing that I see is that boats with smaller sails dont slow down as much when they are going through a tack (where the sail is going straight into the wind and has no lift) because they have less parasitic drag. Im not sure if everyone else with Iceflyer's get this but I just seem to have a really huge wind range using just one windsuring sail and that more than likey is influenced by the twist (or too much twist).

Here's what I understand about twist.. You need it for several reasons. One is that the vortex at the top of the sail (somewhat created by wind moving over the top of the sail from the low pressure side to the high pressure side) can to some extent additinally change the angle of attack of the wind near the top such that the angle of attack is increased. Without some twist, this can lead to a stall at the top of the sail which of course would be a bad thing.

The second thing is that there is a wind gradient under certain conditions where the wind is moving at a lower speed low to the ground and a higher speed higher from the ground. If the boat is not moving at all, the wind will all come in at the same direction which is of course the true wind direction. If the boat were going infinite speed, the wind would also all come in at the same direction which of course would be the direction the boat is traveling. But in between no speed and infinite speed, the apparant wind direction is a vector addition of the boat velocity and the wind velocity. So BOTH the direction and the speed of the wind changes as you get higher up the sail so the sail needs to twist to maintain a constant angle of attack. This is from memory (from a long time ago) but the direction change over the length of the sail peaks somewhere around 2X wind speed (remember that the direction change was zero for no boat speed and also zero for infinite boat speed - so it will peak somewhere between).

2X wind speed is about where a windsurfing sail on a formula board normally operates and that is what the twist in the sail is designed for. However, an ice boat (indluding the ice flyer) typically operate at 3x or 4x wind speed and the aparant wind direction change with hight caused by the true wind speed graident is DECREASED in the 3x to 4x region of operation. So an ice boat typically needs less twist than a windsurfer does.

Good stuff wh. My first sail was an antique 5 meter triangle, no twist. Speed was good and hiking incredably stable. But with nothing but momentum to get around turns, tacking was a rough and clumsy affair.

On "parasitic drag" of sails, how's this sound? Top speed (MPH) = (21m**- sail size m**) X 5 MPH.

Hello Rolley, hope you got in a decent ice boat season!

Regarding the equation for top end of a sail, I dont think it is "linear" with sail area. Here area couple of my data points for top end that Im fairly sure of

9.0 m**2 - about 63.5 mph
5.0 m**2 - 72.5 and possibly around 75 mph

*** see liability disclaimer

With the 9.0, it was probably gusting into the 40 mph range and with the 5.0 it might have been occasionaly gusting to 50 mph (didnt measure the wind but it was a fricken windy day..).

With say a 15 mph wind, the 9.0 would probably be a little faster and with a 25 mph wind, the 5.0 would probably be a little faster and the 9.0 hits the "wall" faster. How you put this into an equation, dont know but I think it would be interesting to do a speed trial and take a bunch of boat speed vs true wind speed measurements for each sail. Wind speed varies all over but you could do a least square fit of the data and get a curve of boat speed to wind speed for each sail and you would see exactly at what true wind speed each sail excelled. This wouldnt take into account the sailing angle relitive to the wind but oh well, it would be interesting (and fun) regardless.

Im am always skeptical of GPS readings as I have personal experience of single GPS readings of max speed being up to 40 mph in error too fast especially when the GPS is in a coat or breast pocket. So I always put the GPS out in front of me away from my moving arms and I also make sure that I get several readings around the peak speed. For example, if I get three peak readings of around 63 mph (must reset the GPS each time) I believe it. I also backup speed readings land sailing with a bycicle magnetic pickup speedometer on the front tire. On the 75 mph reading, I was getting multiple readings a little over 72 mph and one single reading of a little over 75 mph so I "sort of" beleive the 75 mph reading. One of these days, Ill download the GPS data as it is a good way to save the record and peak speed errors are easilly spotted and eliminated.

*** it is dangerous to sail in the high winds required to get this sort of speed!!!