prop to rudde space.

Ok I have a set of shaft's I salvage out of a pace maker they are 19' I need them to go into a GB 50 they are very close to the right size but my question is how much or the max space can I get by with from prop nut to the rudder . I have measure other 50' trawler in the yard and they are running from 12" to 24" and some rudder are flush with the transom and some are set back in 12"-16"

On my 34' Californian the space is about a foot. I would suppose that as the space is increased, steering suffers to some degree, but I doubt it is significant. You dont mention where your struts are. They would have more influence on prop positioning than the rudders. I don't have a long history with inboard shafts, 3 boats total, but all have not had any machining on the tranny coupler other than set screw holes. It would be easy to saw shorter.

prop to rudder

struts can go where ever they need to they are not mounted yet either. what I have seen on the struts is about 6" to 12" in front of the prop's . everything was stolen off the bottom of the boat. so I have to put all new/used stuff back on so I salvaged props,shafts,struts,rudders,and shaft log's. I am putting on new hull on the bottom and so I well have to put new holes in the hull for the struts and rudders. but not the shaft and log holes.

My prop nut is five to six inches in front of the leading edge of my rudder, and I believe this close proximity contributes greatly to the maneuverability.

prop to rudder

I see that the rudder is a good 12 + from the stern. so maybe rudder dosn't make as much diff. as to stern as to prop.

Bear in mind that if the end of the shaft is too close to the rudder, you will have to haul and/or pull the rudder if you ever need to remove the prop.

I have measure other 50' trawler in the yard and they are running from 12" to 24" and some rudder are flush with the transom and some are set back in 12"-16

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Be sure and leave enough space between the end of the shaft and the rudder to slip the prop off.

Some years back there was a very angry man in the yard at Friday Harbor with a bent prop. He had had a new shaft, rudder and strut fitted and the yard that did the work hadn't taken that spacing into consideration. He wacked a prop and had a diver go down to pull the old prop and put his spare on, no can do!! He ended up hauling out in Friday Harbor to pull the rudder off, just to change out the prop.

Larry B

Hopefully you will leave enough room between the prop and rudder that the prop can be removed without pulling the rudder. The rudder may need to be turned one way or the other as mine does. But the closer the better to keep the prop wash going over the rudder as much as possible. Other wise some loss of reaction to rudder input will be lost.
A hole can be put through the rudder to allow for shaft pulling without pulling the rudder.

A rule of thumb for the distance between the strut back edge and the prop hub would be 1 to 1.5 X the shaft diameter. Keep it on the tighter side rather than looser for more support, less vibration.

Didn't actually measure this when hauled, but I would guess it's about 6-8" between the prop nuts and the rudder. Note that the rudder pivot point is offset and there's a hole in the rudder to accommodate removing the shaft.

dvd

Another consideration on boats where the keel extends under the prop, as in the photo posted by DVD, is that the blade tips not come too close to the keel. Water coming off the tip of the blade can blast a crater into the top of the fiberglass keel just under the blade tip. I found out the hard way when I put a prop on with just about an inch of clearance. It wasn't dangerous but I did repair it with epoxy putty and put a strip of metal over the spot.

you may want to check in at "boatdiesel.com" where questions such as yours are common and the posters include professionals.