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Go Back   SailNet Community > On Board > Gear & Maintenance > Bow thruster - theoretizing :)
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Thread: Bow thruster - theoretizing :) Reply to Thread
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Topic Review (Newest First)
07-10-2008 08:05 PM
SVAuspicious
Quote:
Originally Posted by sailaway21 View Post
Dave,
I can understand your concern about hydrodynamics in a sailing vessel and the effects of a bow thruster tunnel on them but as someone who went to a school not too far from Webb, Kings Point, I'd be most interested in hearing about any merchant vessels with bow thruster doors, having never encountered a one in twenty years at sea. Grating to prevent lines and debri from being ingested yes, doors no.
You're going to make me blow rust off that part of my brain aren't you? My library is all in storage. I think the SL-7s all had doors. I think most of the ULCCs I came across did also. Certainly the MSC ships I worked on all did.

Quote:
Originally Posted by brak View Post
I am in Solomons, MD - if you are ever in the area, drop me a note and come by
I might be through in late July or early August depending on wind and a business trip. I usually anchor up by the Holiday Inn so I can visit friends and walk to Woodburns.
07-10-2008 10:22 AM
brak
Quote:
Originally Posted by sailaway21 View Post
Sure sounds like a right hand screw. By "harder turning to stbd" I assume you mean not as effective turning moment. Any chance the screw is offset on that particular boat?
"Harder turning" means I have to exert more effort when turning the wheel to stbd. - which means there is more force operating on the rudder, that I have to counteract. Much more - hydraulic usually lacks any feedback - when sailing it is absolutely not possible to tell what the rudder is doing other than by looking at the autopilot rudder indicator or waiting for the turn to occur, and check visually.

The prop is dead on center, comes right out of the middle of the rear portion of keel, sits in an aperture between the keel and the rudder.

Well, guess it's right hand all right. I wonder why the thing turns the wrong way, then. It's a mistery in its own right
07-10-2008 02:31 AM
Stillraining Thats just plain screwy ...
07-10-2008 01:04 AM
artbyjody
Quote:
Originally Posted by sailaway21 View Post
Sure sounds like a right hand screw. By "harder turning to stbd" I assume you mean not as effective turning moment. Any chance the screw is offset on that particular boat?
What direction of the screwing is nearly not as important as the direction of the actual screw afterwards...resul;ts are the same I think..
07-10-2008 12:53 AM
sailaway21
Quote:
Originally Posted by brak View Post
BTW. another curious handling effect is that when I am moving under power at high speed (6-7 kts), turning to stbd is much harder than turning to port (and it means there is REALLY something that makes a difference, as usually hydraulic steering has 0 feedback). Under sail at the same speed - no such effect, both sides are equal. Must be something about how prop wash is hitting the rudder.
Sure sounds like a right hand screw. By "harder turning to stbd" I assume you mean not as effective turning moment. Any chance the screw is offset on that particular boat?
07-09-2008 11:12 PM
brak
Quote:
Originally Posted by SVAuspicious View Post

Brak, where are you located? If you aren't too far away I'll sail or drive up and we can play and find something that works for you. I'm in the middle of the Chesapeake Bay.

Something does sound odd, but you have a good boat so we all should be able to help you get in and out of your slip without undue stress.

sail fast, dave
I am in Solomons, MD - if you are ever in the area, drop me a note and come by
07-09-2008 11:10 PM
brak BTW. another curious handling effect is that when I am moving under power at high speed (6-7 kts), turning to stbd is much harder than turning to port (and it means there is REALLY something that makes a difference, as usually hydraulic steering has 0 feedback). Under sail at the same speed - no such effect, both sides are equal. Must be something about how prop wash is hitting the rudder.
07-09-2008 11:05 PM
brak
Quote:
Originally Posted by Plumper View Post
Is there something different about your HR 35 compared to others? If they were all like that you would think that the owners would be discussing the difficulties somewhere. I think there is something odd going on. 7 turns lock to lock seems excessive as well. My 33 footer is two lock to lock. How far does the rudder go over at the lock?
There really aren't too many HR 35s out there. While they presumably built over 700, only under 200 or so made it to US. Since they are all at least 30 years old now (with mine being one of the oldest) many are pretty much idle, sitting there. There is one person on this forum with a boat like mine, and that's the only active Rasmus owner I know of. There is one more Rasmus in a marina next to mine, but it looks like that boat haven't left its dock in a long long time. A few are for sale, and been that way for at least a year or two, not moving either. There is a UK based owners group with one or two messages a year. That's about it. So, I am not sure there is much to go by.

And yes, the boat is very different from most sailboats. Hydraulic steering is a rarity on a sailboat in general, and on a sailboat of this size in particular. Just that alone creates very different handling characteristics from your average 33 footer (to which I can attest, having sailed quite a few of average 33-36 footers or so).

With hydraulic steering there is usually many more turns lock to lock than there are with mechanical. This is a function of pump size (i.e. how much hydraulic fluid volume it moves per turn) and size of the ram (cylinder) that is pushing the rudder. Ram size is governed by rudder size (it needs to be sufficiently large to create appropriate force), and steering pump size is governed by what human can do by hand (powerboats usually have power assisted pumps). There are a bit less than 7 turns and I can get by with 2.5 each way, but in any case going from one side to the other is slow (and having to change gears using separate handles for gear and throttle does not help either, if you dont have 3 hands).
07-09-2008 10:17 PM
TomKeffer What kind of prop do you have? Some are much better in reverse than others.

I had a bowthruster on my old boat and while it helped in tight situations, it does come at a cost. What I disliked the most is the way it sat in the middle of the sail locker under the forward berth, making it very tough to get sails in and out. Also, there's a lot of weight and complexity involved, particularly for a 35' boat.
07-09-2008 05:33 PM
sailaway21 Absolutely correct, pamlico.
If you're to traipse about the ocean as a cruiser it probably is a needless expense of limited marginal utility. If you are restricted in where you can keep your boat and that place has tight confines and your boat meets all your other needs rather well it would seem foolish to not have one and use up potential sailing time with risky and time-consuming manoeuvring at the beginning and end of each voyage.

Heck, some people even pick different colors for their boat now, I hear.
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