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Friday, June 5, 2020

Extended running gear

Early on in our build I talked about a few of the things we are doing a bit differently, and one of them is to extend the running gear.  When the 64 became the 68, the position of the prop and rudder weren't moved.  The 68 has enjoyed great success so this clearly isn't a problem, but early in our process I got to talking with Jeff Leishman (Nordhavn boat designed) about this and he suggested we could extend the gear by adding a strut.  They have done exactly this when going from the 86 to the 96, and the results were quite good.  By pushing the rudder aft it gets it further out of the "shadow" (turbulence) of the keel and into smoother flowing water.  The result is less cavitation, less turbulence, greater efficiency, and less vibration.  After a bit of hemming and hawing, we decided to go ahead with it.  Moving the prop further aft also results in moving the rudder further aft, and that should improve tracking and reduce susceptibility to broaching.  All sounds good, but of course only time will tell the full story.

Only a week or two after our visit in December 2019, the strut and shaft were installed.  The strut is Y shaped, anchoring to the hull in two locations, and the shoe below.  Normally the prop is right where the shaft exits the keel, but in this arrangement it's between 3-4 feet further aft.


Extended running gear "Y" strut


Extended running gear with shaft installed


Inside the laz where the steering gear is located, you can see the rudder post and supporting trestle is back nearly against the transom.   The structure forward of that (closer to where the picture is taken from) is the structure that the steering cylinders anchor to.  This arrangement makes it a bit easier to fully utilize the space in the laz, so another benefit to the change.


3 comments:

  1. Peter, when we first met, you said "when you've seen one Nordhavn, you've seen one Nordhavn. I think your insight and specialization puts you in league of your own! Thanks for sharing.

    ReplyDelete
  2. Peter, what did you end up doing on the starbord side hull steps to facilitate dingy boarding ? Thanks.
    Whit

    ReplyDelete
    Replies
    1. Nothing more at this point. Until I can somehow climb up and down to try it, it's just speculation about what will work. Maybe if I can get back to the yard, and maybe if there is sufficient scaffolding I could try it out. But it's a long way down so I'm not taking any chances. And even if I have had a chance to try it, I won't fit any grab rails or handles until we are commissioning the boat back in Florida.

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