Hi Franklin,
Not wishing to steal Glenn's thunder but herewith some info which may be of use:-
1) Jim Bohart (of Hunters) once gave an interview with CWBB (Cruising World Mag?) in which he outlined Hunter's processes. The item below is an extract from this interview in which he notes that the wound stock is more than 50% stronger than the steel version and there is no stainless inside to suffer crevice corrosion or fatigue. He told me they destroyed their rig whilst testing it.
I do not know when this was published but I believe that at some time rudders were put out to 'Fosse' - maybe they still are?
The philosophy of making the stock so much stronger raises two issues. First should it hit something which is immovable and which missed the keel then the stock would break off rather than just bend. Of course the boat wouldn't leak but there would be no steering nor any hope of it. A bent steel stock would still mean no steering but also possibly no way of making the boat go straight either. Yer pays yer money and yer takes yer chance.
The second issue is if the stock was so strong it took the ass end out of the boat!
2) I just scanned a faded yellowing fax I was sent in 1998 when I was asking the same questions. If the .jpg compression needed to put it up on this site causes too much loss of detail please e-mail me and I will send you the full file which is 1.5 Mb.
3) For info the rudder stock is 6" diameter at the lower bearing and either 3" or 4" dia at the top. The bearings in the rudder tube are UHMW (Ultra High Molecular Weight Polythene) which is an excellent low friction non-water absorbing material and the stock has stainless tubes bonded on as journals. The bearing area is enormous as compared to 2" dia stainless, so they should last several lifetimes - yours plus mine!
Because the stock extends so far into the rudder, and is so large in diameter, there is plenty of material to make a bond to the rudder half shells. I would not expect this to fail and, there being no metal, it will not rot either.
BTW; You need a loose fitting 6" ID collar slid on the stock between top of rudder and small skeg on hull to stop the rudder from floating up and jamming against the skeg.
My collar was too short and I replaced it with a 1/2" length of uPVC sewer pipe. I sawed across this at one point to be able to open it up and clip it on the stock and it now has a 6" dia jubilee clip as a retainer.
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Q & A with Jim Bohart, Hunter Marine - continued (3)
We make our rudders and rudderposts on site. The rudder skins are made with bi-axial stitched glass and vinylester resin. The tubes are made of a series of uni-directionals wrapped around a Mylar skinned balloon bolted into a mold and compressed with low pressure air till cured, (the Mylar wrap eases removal of the balloon). The post is then glassed into the rudder to a depth of 3/4s of the depth of the blade and all voids are filled with urethane foam. Destructive testing on a 40.5 rudder and compared to a 1/4" dia. 4" stainless post and ss webbed blade accomplished some interesting results. The blades were placed in a jig bolted to the floor and brought under strain with a winch connected through a 4" hole in the lower part of the blades, a load cell placed in line recorded the results: at around 6000psi the frp and stainless structure collapsed. At over 9000 psi the jig containing the composite structure collapsed, The composite structure survived the test. We've been using this system for the past 5 years and the rudders have proven to be lighter stronger and non-corrosive. We tested them in Charter fleets prior to introduction in the general market.
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