Fish tail rudder idea!!!

[geoleo]

My idea is to make 2 TEAK wedges of 1 X 6 inch size the full height of the aft rudder edge and epoxy glue and bolt it thru ss plate rudder to each side. This goes on my 1982 MT34 . Sand and paint to suit. This will avoid high welding costs and be complete DIY except for wood shop costs.

 

[Simi 60]

If its a S'S rudder its a 10 minute job to weld angle on trailing edge with 308l rods and $150 arc welder.
Added bonus, you now have an arc welder

 

[Steve91T]

No way would it be strong enough.

 

[psneeld]

No way would it be strong enough.

What the teak wedges?

I am guessing done well they would be fine.

My concern would be erosion (unless that is what you meant)....but nothing some epoxy every couple years couldn't handle unless putting a thousand or more hours on it every year.

If something happens to them, no big deal...easy and inexpensive to replace or remove temporarily.

 

[healhustler]

Well, if teak would work, why not starboard?

 

[Steve91T]

What the teak wedges?

I am guessing done well they would be fine.

My concern would be erosion (unless that is what you meant)....but nothing some epoxy every couple years couldn't handle unless putting a thousand or more hours on it every year.

If something happens to them, no big deal...easy and inexpensive to replace or remove temporarily.

Yeah maybe. It’s a lot of force and I can just see them snapping off with one hard turn or two. And by the way, I’m basing my opinion on absolutely no experience what so ever, so there’s that.

 

[boatpoker]

DIRT FREE was extremely difficult to turn at low speed ..... Stainless steel plate bent at 15 degrees and through bolted to the rudder made a huge difference in low speed manouverability. I installed them perpendicular to the thrust.

 

[Sabre602]

Anything could be through-bolted to the trailing edge of a rudder...it doesn't have to be teak. I'm not sure that the epoxy would be necessary and, in that application, that it would contribute much for very long.

If a variety of zincs stick on to a rudder, why not the trailing edge fish tail? The tension force on such bolts would be negligible, the shear forces minimal.

If a solid wedge of teak, why not try it? But honestly, a couple of bent metal plates as shown in boatpoker's picture would cost less to fabricate.

 

[geoleo]

Well, if teak would work, why not starboard?

Good idea except might not hold the anti foul paint!

 

[geoleo]

DIRT FREE was extremely difficult to turn at low speed ..... Stainless steel plate bent at 15 degrees and through bolted to the rudder made a huge difference in low speed manouverability. I installed them perpendicular to the thrust.

"NICE!!! Did it improve straight tracking any ???

 

[geoleo]

If its a S'S rudder its a 10 minute job to weld angle on trailing edge with 308l rods and $150 arc welder.
Added bonus, you now have an arc welder

Thanks! Then I would have a welder to move -store and sell----

 

[twistedtree]

Wouldn’t the flare created by all these approaches create a bunch of drag under normal operation? I suspect that’s why it’s more common to see articulated rudders?

 

[Nomad Willy]

Twist,
I agree.
The propwash is way above boat speed. I moved one of my zincs up to the top of the rudder to get them out of the propwash.
As we used to say in aviation the propwash is trying to blow the tail backwards. So it pulls back on the fuselage. Rudders pulling back on boats dosn’t help efficiency.

 

[Xsbank]

I have a single engine no bow thruster and struggled with controlling the bow in a crosswind. I had a 3 1/2” angle welded to the trailing edge of my rudder and there is no loss of cruise speed, less vibration at cruise and superior low-speed control. I use a welder to attach my anodes so it only cost me another $100 to have this attached and that included the cost of the aluminum. The only part that slowed the process was figuring out how to hold the angle in place symmetrically for the welding. Make it a serious connection or you risk losing the doodad you use. Otherwise think of the consequences if it detaches while backing down. All those other ideas are too flimsy.

 

[psneeld]

The million dollar question...

How big of a fishtail to improve turning but small enough to be insignificant drag at cruise?

 

[MurrayM]

The million dollar question...

How big of a fishtail to improve turning but small enough to be insignificant drag at cruise?

Good article below, with enough hints to track down Dave Gerr's article on Thistle, MacLear, Fishtail, and/or Schilling rudders;

https://www.sailangle.com/group-forum/topic/id/1871

 

[Seevee]

DIRT FREE was extremely difficult to turn at low speed ..... Stainless steel plate bent at 15 degrees and through bolted to the rudder made a huge difference in low speed manouverability. I installed them perpendicular to the thrust.

Did a rudder mod VERY similar to your, fabricated two pieces of stainless, 6 in wide, bent the aft 3 in at 30d. Bolted it to the rudder tail and did improve steering, however, not quite as much as I wanted. But, when I get aggressive to modify it again, it will be dirt simple and just unbolt the mod, make a new one with the same hole pattern and bolt back on.

Might use aluminum if I try it again... softer, yes, but significantly easier to work with.

 

[Simi 60]

Thanks! Then I would have a welder to move -store and sell----

Mine takes up less space than 1/2 carton of beer.
Stays onboard and is rarely used but invaluable when needed and saves a fortune in paying someone not to mention finding someone to do a relatively simple task.

 

[Xsbank]

I’m not sure where you are getting this high cost for a weldor, they are quite reasonable. However, if you are looking for a fabricator to build something, now it can get spendy.

How much drag do you think is produced by a small piece of aluminum behind a 36” wheel travelling at a max, balls-to-the-wall 10 knots? None of us are driving Americas Cup yachts on here. I’ll bet it’s way less drag than towing your dinghy.

 

[boatpoker]

"NICE!!! Did it improve straight tracking any ???

Zero effect on tracking which was not an issue to begin with. It did help a bit when backing up.

2 pcs stainless bent at 15 degree. 2 ss bolts & nuts, one drill bit. 1hr. installation and about $100 Cndn dollarettes, I believe that's about ten bucks US

 

[boatpoker]

Might use aluminum if I try it again... softer, yes, but significantly easier to work with.

If your rudder is ss, your aluminum plates will disappear through galvanic corrosion.

 

[boatpoker]

Twist,
I agree.
The propwash is way above boat speed. I moved one of my zincs up to the top of the rudder to get them out of the propwash.
As we used to say in aviation the propwash is trying to blow the tail backwards. So it pulls back on the fuselage. Rudders pulling back on boats dosn’t help efficiency.

No noticeable loss of efficiency or fuel consumption at 7 knots (as measured between Toronto and Bahamas), actually no noticeable difference in any way except the ability to do tight turns at low speed and a moderate improvement going astern.

 

[MurrayM]

...about $100 Cndn dollarettes, I believe that's about ten bucks US

Been cruising in the ‘ol US of A?

Your dollar is worth a dollar in BC...you should come up & over, down and around, or across at 100kph for a visit

 

[boatpoker]

Been cruising in the ‘ol US of A?

Your dollar is worth a dollar in BC...you should come up & over, down and around, or across at 100kph for a visit

+2

 

[Lepke]

There is a commercial rudder addition made for single screw ships, tugs and large commercial boats. About 20% more rudder tail is added with pivots and linkage so in a turn, the further the rudder goes toward full, the further the extension moves. I've seen a homemade one with ss cables and attachments along side the rudder post. A ship will make a turning circle about 20-25% smaller.

 

[geoleo]

The million dollar question...

How big of a fishtail to improve turning but small enough to be insignificant drag at cruise?

Guesswork

 

[boatpoker]

Guesswork

It is guess work but easily and inexpensively changed if bolted on. A buddy who is a naval architect saw my effort after the fact and said my 6" fins at 15 degrees on a 38' displacement hull was right about what he would have prescribed.

 

[Sailor of Fortune]

There is a commercial rudder addition made for single screw ships, tugs and large commercial boats. About 20% more rudder tail is added with pivots and linkage so in a turn, the further the rudder goes toward full, the further the extension moves. I've seen a homemade one with ss cables and attachments along side the rudder post. A ship will make a turning circle about 20-25% smaller.

Articulating rudder, a very different animal than adding to existing rudder.

 

[O C Diver]

If you want great slow speed turning, the 3 components to success are:

A large rudder.
A significant leading edge (up to 28% of what's behind the pivot point, put in front of the pivot point). Without a leading edge, you lose half of the prop wash.
Being able to pivot the rudder 40 degrees.

This is the rudder on my trawler. It's a foil style, designed for slow speed. There is a significant leading edge and it will pivot 40 degrees. You can push this boat sideways by pivoting the rudder hard over, going forward at idle and pushing the bow with the bow thruster. There is an incredible amount of sideways push with this rudder hard over!





This is the rudder we built for my Bruno & Stillman. Large leading edge and 40+ degree pivot. This boat turns on a dime and gives you a nickel back.




Ted

 

[BeeJay]

I made a similar rudder mod but also added end plates. My thoughts were that it would help prevent the water taking a short cut and bypassing the rear strip. It has had a massive effect on the hull and I am still evaluating the effects. It must be costing fuel as there seems to be a lot of ocean chasing the boat about the harbour that there wasn’t before, and the wake leaves the hull from further back on the sides of the hull. Steering is much more direct and low speed manoeuvring has improved ten fold which was expected (planed -hoped more likely). What I didn’t expect was a higher top speed and the hull traveling much flatter. It’s intriguing and got me thinking of removing it next season so I can make more accurate comparison as I didn’t make enough observations of the earlier set up. I think what may be happening with the increase in top speed is that the schilling strip is dragging a lower pressure behind the rudder that is being filled by water that would of otherwise continued to travel below the keel and rudder. This upward movement of water I suspect is creating lift at the large flat area at the stern and keeping the boat bow down increasing the effective waterline. The bow stays flat at all speeds so it will be interesting to see if it climbs over big seas on the bow or attempts to punch through them ??. I’m really surprised at what a huge change something so subtle can make. I suspect the designer would be horrified at what I’ve done but gosh it’s interesting. I can post a couple of pics if anyone’s interested. I would also be interested on anybody’s ideas on what’s really going on.