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Boat Forum / Building / October 2005Variable Pitch Props
I'm in the process of building an e-boat and am looking for a ~19 inch variable pitch prop along with probably the shaft and any controls that may be associated with it. A friend of mine told me that Volvo makes one, but none of their dealers seems to know anything about it. If anyone knows of a source, it would be greatly appreciated. Hi What exactly are you looking for --- an adjuatable pitch prop. or a variable pitch prop, going forth and reverse as in old fishing boats ? Both cases you are to put down quite a sum, the adjust pitch are rare and expensive the fishing boat types are usealy only two blades and only few manufactores make these and only to fit onto their own motors , if 3 blades they cost more than 3 gearboxes all together and you still need the piece to do the pitch move. ------ what is an e-boat ? > Hi > What exactly are you looking for --- an adjuatable pitch prop. or a > variable pitch prop, going forth and reverse as in old fishing boats ? Something like that with ~19" blades would be perfect. > Both cases you are to put down quite a sum, the adjust pitch are rare > and expensive the fishing boat types are usealy only two blades and Two blades would work fine. > only few manufactores make these and only to fit onto their own motors > , if 3 blades they cost more than 3 gearboxes all together and you > still need the piece to do the pitch move. ------ what is an e-boat ? I'm converting a 38' ketch from a diesel engine to an electric boat using twin inline eteks. Hi The Sabb diesel engines was two blades and you could order pitch propellor that leveled the blades for use in sail boats , --- this was a rare but usefull combination for pitch propell but there was some marked for pitch propellor in this application and you could maby find one second hand in scandinavian boats markeds --- >From what I remember the bigggest Sabb with pitch propellor was 22Hp maby 30 Hp but the trust bearing are build into the propellor mounting outside the boat and the pitch are done by moving the propellor sharft fore and aft just a few cm. Bigger pitch propellor without build in trust bearing, had a hollow sharft with a movable rod at the center to turn the pitch. I don't know if the Sabb engines are even manufactored anymore but a lot are around as they are reliable reasoable slowrunning engines build for boats, and then ofcaurse there must be some propellors with sharfts around from worn out engines ,but please remember that even you get a trust bearing with the propellor ,you still need some mechanic to force the sharft to make the propellor "turn". > I'm in the process of building an e-boat and am looking for a ~19 inch > variable pitch prop along with probably the shaft and any controls that may > be associated with it. > > A friend of mine told me that Volvo makes one, but none of their dealers > seems to know anything about it. Do a google for a boat named Bandersnatch. It is a 63 ft ferro built by a guy named Norm Johnson. (He is on the live-aboard list) He installed what you want. The equipment is from Scandinavia. Lew Hi I used to have a small boat with a Sabb engine. the guy who ran the UK dealership has now retired but if you contact the makers direct they may be able to help you. regards Peter. (5 years ago I did what I said I would never do! I bought a 45 year old wooden boat. Still working on it!) Sabb Motor P.O. Box 7170 5020 Bergen, Norway www.sabb.no Phone:+47 55 34 88 00 Fax: + 47 55 34 88 01 firmapost@sabb.no > I'm in the process of building an e-boat and am looking for a ~19 inch > variable pitch prop along with probably the shaft and any controls that may [quoted text clipped - 4 lines] > > If anyone knows of a source, it would be greatly appreciated. I know this isn't the answer to your question, but it does give me a chance to mention the variable/reversing pitch system used on a few Navy and some commercial ships that require quick response in maneuvering. The diesel engines drive into a reduction gear (and only have a clutch to disconnect an down engine). The prop shaft run out of the independent gear box where the thrust bearing is normally located. The prop is has a hub with hydraulic mechanisms that rotate the synchronized multiple blades from either side of "0" pitch (neutral) to fwd or reverse. The hydraulic control of this blade assembly comes through an Oil Distribution Box (OD Box) on the extreme inboard end of the prop shaft. The shaft end rotates inside this box and the hydraulic oil pressure is transmitted down two passages bored from this inboard end, down to the hub end where it is can act on the prop blade mechanism to rotate the blade. This may sound overly complex but it eliminates the need to stop and reverse the engines while maneuvering. Much less complex than reversing gears for engines of these HPs. The one problem I encountered while dealing with these system was from total loss of hydraulic pressure. The prop blades seem to have a mind of their own and as long as the engine is running/engaged the prop continues to rotate and may switch from "0" pitch to full astern (my experience) or full ahead.  SignatureMy experience and opinion, FWIW -- Steve s/v Good Intentions That sounds like the system used on aircraft (except for the reliability). At ten grand or more per propeller, I doubt it's what he's looking for. Roger derbyrm@NOSPAMearthlinkNOSPAM.net http://home.earthlink.net/~derbyrm <snip> > The prop is has a hub with hydraulic mechanisms that rotate the > synchronized multiple blades from either side of "0" pitch (neutral) to [quoted text clipped - 15 lines] > to rotate and may switch from "0" pitch to full astern (my experience) or > full ahead. Hi Steve this was the exact system with 99 pct. of the old Semi diesels in commersial and fishing vessels --- it is great when manuvering as both reverse and forwerds turn the aft end of the ship in same direction ; going forwerds and reverse a number of times, simply turn the boat on a coin , when you back out a harbour you can plan your manuver way ahead and kindof feel how perfect you navigate 36 ton just with a turnable pitch propellor a clutch a rudder that make just the final touch man you can almost make it fly ;)) Anyway there was no hydrolics to turn a maby one meter diameter two blade with a flywheel with one ton deadweight and just two cylinders the sice each of a bucked . Now these engines are still used but not many are still manufactored ,and that even they are such engines that will run to the ends of day's at 400 rev. Sabb copied the best of it all with their small engine with fast reverse ; 3/4 rounds from fore to aft, without clutch and is proberly the best thing to look for ; emagine 2 each side the boat, then you can make it go sideverds ( I could with just one ;)) The Navies of the world, seem to spare no money in complicated propulsion systems in their ships. My primary experience was with the patrol gun boats (PCs and PCGs) of the Saudi Navy which had two MTU diesels and a LM-2500 gas turbine into a single gear box. Each was clutched in or out and could drive the twin shafts. Diesels for normal cruising and the gas turbine for high speed. The neat thing about this system (single gear box) with controllable pitch on each shaft, was to maneuver just like a the shafts had independent prime movers. While in fact the gas turbine or the diesels could be dividing power to each shaft or sending all the power to one shaft. (I should note that the gas turbine was never operated with the diesels (or vise/versa). Another old school twin scew system I always thought was great, coming from WWII technology was the PCs we gave to the Cambodian Navy in the '60-'70s. These were independent reduction gears on each shaft, however there were four V-8-71 engines on each reduction gear. Each engine was clutched in or out and at low speed they could run on one engine per shaft. (The configuration was 2 engines facing forward and 2 facing aft, each coupled to their independent pinion gear.) Normally the 8 twin disc clutches were pneumatically controlled but the one ship I was onboard, while the Cambodian Navy was turning them back over to the US Navy, had no air compressor working and the engineman was setting on the reduction gear and "answering bells" manually. When this particular ship arrived in Subic Bay, loaded with refuges, they only had one engine running on one shaft and 2 running on the other. Main generator was down and they were power the steering and navigation gear with a 25 KW aux. gen set. Just some memories from the (good) Ole Days. Steve s/v Good Intentions > Hi > [quoted text clipped - 17 lines] > the best thing to look for ; emagine 2 each side the boat, then you can > make it go sideverds ( I could with just one ;)) |
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