Larry just to give prolong the headache, Harbor freight advertises an underwater camera foe 99.00 includes plenty of cable ,but no monitor. I f you really wanted to know what goes on under the boat :-) . Our water is not clear enough, visibility is about 2-3 ft. But I often have thought this was a good way to check your center board condition.
gilbert -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Larry E Yake Sent: Monday, November 28, 2005 11:48 PM To: [email protected] Subject: Re: M_Boats: New Kick up rudder Wow, Tod, nice bit of research work. I didn't have to go to the 4th website to get the headache. Not being an engineer, and not even playing one on TV, it's mostly over my head, but I follow your examples of forces somewhat. I'm sure I don't understand all the forces at work on a boat rudder, knowing only what I feel and the results I see. As you mentioned, the "feel" can be deceiving. It would be interesting to be able to look down the rudder under various conditions to see if there were some mysterious things happening. Nice thread here. Good discussion. Larry On Tue, 29 Nov 2005 00:04:17 -0500 <[EMAIL PROTECTED]> writes: > Larry, > > I wasn't thinking about torque from weather helm, but instead a > twisting of > the blade due to the force on the blade from the water not being in > line > with what structural engineers call the "shear center". You might > not even > particularly feel any weather helm, depending on how well balanced > the > rudder blade is. Sometimes you get funny things like that going on. > For > example, if you have a 10' long piece of angle iron sticking out of > a wall, > looking like an "L" and you put a sandbag on the end of it, it > won't just > bend down a bit. It will also bend to one side. Similarly, if you > have a > 10' long piece of channel sticking out of a wall like so: [ and you > push > down on it at the centroid of the cross-sectional area, it will not > only > bend down a bit but it will also twist. To get it to bend straight > down, > you actually have to put a little bracket on the backside of the [ > away from > the horizontal legs (flanges) and push down there (to the left of > the > vertical web as I typed it) or else counter twist as you push down. > > I was curious so I googled the modulus of elasticity of some > plastics like > HDPE and UHMW and Starboard and it looks like they are quite a bit > (about 10 > times) more bendy than the same section built of mahogany. > > http://www.machinist-materials.com/comparison_table_for_plastics.htm > > http://www.righteouswoods.net/mahogany_african.html (probably our > rudders > are Honduras Mahogany, I'd guess, but this gets us in the ball > park) > > However, that still doesn't mean that the rudder couldn't give > quite > satisfactory performance. It could be that in both cases the > deflections > are not especially significant. If I were racing, though, I'd > choose the > wood any day over an unreinforced plastic, unless the course were > through > some skinny water! :o) > > I'm still wondering about the location of the shear center of a > foil, > though. Didn't see anything really juicy. Here is a brief mention > of the > subject: > > http://www.eng.auburn.edu/~drmac/elasticaxis.html > > If you wanna give yourself a headache, look at this one. Sure gives > me one: > > http://www.ae.msstate.edu/~masoud/Teaching/exp/A15.7_8_ex1.html > > The thing is, your typical foil such as an airplane wing isn't made > of a > homogenous (sp?) material the way our rudders are. > > Anyway, not knocking them; for some places they make much better > sense than > the standard non kick-up rudder. > > Tod > M17 #408 > BuscaBrisas > > -----Original Message----- > From: > [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] > On > Behalf Of Larry E Yake > Sent: Monday, November 28, 2005 8:19 PM > To: [email protected] > Subject: Re: M_Boats: New Kick up rudder > > > Regarding the Ida Sailor kick-up rudder, I would think you would be > experiencing a huge amount of weatherhelm before you had enough > torque to > make the rudder blade twist. The cheek plates are pretty > substantial. I > really doubt we're getting any twist or flex. The tiller doesn't > have any of > the flex feel that I've noticed on the stock M15 kick up rudder. > I've only > been using mine one season so I can't speak to the long term > durability > issue other than to say the quality and strength of construction > look very > good. The pointing ability doesn't seem to be any different than the > stock > rudder, which is a good thing. My stock rudder was one of the > earlier, > balanced models and I was reluctant to replace it, but since it > couldn't > even be raised vertically in shallow water I needed to do something. > The > foil shape is very good on the stock 17 rudder, so I was pleased > that the > kick-up rudder seems equal in performance. I have no vested > interest in Ida > Sailor, and get nothing from them for endorsements. I did get a > discount on > my rudder for helping with the design. I just believe it's a good > product. > The rudder breaking on the Santana is somewhat worrisome. I have > also heard > of a corrosion problem on the aluminum cheekplates on one of the > east coast > boats, which was also blamed on substandard material. There are > about a > dozen Ida Sailor M17 rudders out there last I heard. Anyone else > having any > problems? > > Larry > > On Mon, 28 Nov 2005 19:32:55 -0500 <[EMAIL PROTECTED]> writes: > > While those plastics no doubt offer some advantages, I would > suspect > > that > > rigidity of the overall blade would be less than the factory > rudder, > > meaning > > that when viewed from the top the tip of the rudder would want to > > > bow to > > weather with weather helm and might well twist, putting the tip at > > > a > > different angle of attack than the upper part of the blade if the > > > shear > > center of the foil doesn't coincide with the center of lift, which > > > could > > offset some of the gains of the "good" foil shape. Still, for > some > > people > > it's probably a very good option, certainly better than getting > your > > transom > > bolts popped. > > > > Tod > > M17 #408 > > BuscaBrisas (<= who's transom bolts got stretched significantly > > once) > > > > > > -----Original Message----- > > From: > > [EMAIL PROTECTED] > > > [mailto:[EMAIL PROTECTED] > > > On > > Behalf Of Tom Smith > > Sent: Monday, November 28, 2005 12:34 PM > > To: For and about Montgomery Sailboats > > Subject: RE: M_Boats: New Kick up rudder > > > > > > > > Larry has an Idasailor rudder, Randy Graves has one, and I have > one > > that's > > not yet installed. I'll let those guys speak regarding durability > > > over time > > and performance, but I'm impressed with the quality of the build. > I > > wasn't > > aware of a new, lighter version, or if the Montgomery blades can > be > > ordered > > in a different hdpe material than what I got or not. It sure > seems > > industrial strength to me, and in my opinion it's a superior > > solution to > > grounding than the original slide-up design. > > > > t > > > > > > > > /)) Tom Smith & Jane VanWinkle > > M15/345--Chukar > > M17/496--Unnamed > > > > > > > > > > > > _______________________________________________ > > > http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats > > > > > > _______________________________________________ > > in/mailman/listinfo/montgomery_boats > > > > > > _______________________________________________ > http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats > > > _______________________________________________ > http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats > > _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
