Unusual rudder placement

[Lynton Banks]

Hi guys Newbie here .
Following on from this thread rudders were discussed.
Lifting strakes do they produce lift in the submerged sections https://www.boatdesign.net/threads/lifting-strakes-do-they-produce-lift-in-the-submerged-sections.67770/

Picking up on the rudders I thought folks might be interested in this set up .

This boat pre dates mine .In other words when production of the 46 ceased the 42( renamed 48 ) followed for there mid range.It was also used mid 90 s on the 54 or maybe the 56 the next size up . So he was pretty keen on this design.

He dropped them on the 60 went back to his hanging rudders .

What was the rationale for this movable rudder bar .
Drag reduction ? Or ……

 

[sharpii2]

My guess is to keep the rudder axis perpendicular to the water surface. As the boat gets on a plane, the bow rises and the stern squats a bit. It is at this point the planing starts to happen (or is supposed to). When it does, the somewhat squated stern starts to rise, and the boat levels out a bit. But not entirely.

 

[fallguy]

I will only comment as a boat lover. @baeckmo is really smart; so if you get to hear from him, consider yourself fortunate.

The picture is interesting. It looks like they are pulling the rudders up to help reduce drag coming out of the hole, then once the boat is up, can bump down to get some rudder back. The leading edge of these rudders seems pretty big to me, as a casual boat lover and not a racer.

For private use boat; seems like a lot of monkey business versus a rudder with a longer tail that would stay in the water when the boat is up or one more streamlined on the leading edge and with a different trailing edge on top.

See if the experts coin in. Thanks for the contributions to the forum, really fun stuff.

 

[Lynton Banks]

Here’s another pic of the 54 .To help with deliberations .Yes the upper stock is pretty thick to house the bearing shaft .
It appears round at the leading edge .
The top of the blades have a little collar too ?

Why would he design them like this ? interesting to find out .He did a long run of boats with these .
The props hang just behind the transom too necessitating those fixed planes / flaps on both the 46 and 54 .Note they have little vertical down pieces at there ends .Any ideas any one ?

The 54 ^

 

[jehardiman]

This look like a pretty expensive fix to the original problem they had, but does have the ability to experiment a bit. I don't think the hull was originally designed to have wheels that size in that location. On second thought, perhaps that is exactly what this is, a research set up for a new hull.

 

[Blueknarr]

Looks to me like a series of power/speed enhancements.

First drive shaft lengthened to allow for larger prop diameter.
But this didn't allow room for rudder post within the hull.
Easy solution is to have rudders well aft of transom on the extendo bracket.

 

[Lynton Banks]

Looks to me like a series of power/speed enhancements.

First drive shaft lengthened to allow for larger prop diameter.
But this didn't allow room for rudder post within the hull.
Easy solution is to have rudders well aft of transom on the extendo bracket.

That’s what I was thinking .
The 54 in the 1990.s with V 12 MAN s and the Hp of the day 1100 or 1200 ? Would reach 40 knots .The 46 had 800 Hp motors pushing 24 tons .

Suppose ideally we need an owner ( plenty of survivors) to tell us if dipping or lifting them speed is worthwhile .

 

[comfisherman]

That's a lot of added complexity to what is traditionally a very simplistic machine.

Only two reasons to introduce that; chasing absolute performance or to cover up a fairly brutal design flaw. Guessing by your numbers the former is the case.

Always interested to see what the pleasure side of things does, such a different world.