Cut the rudder??

[Don C L]

I'd be more careful about where I anchored rather than cut my rudder. I say leave the rudder alone.

[coopec43]

Originally Posted by Don C L

I'd be more careful about where I anchored rather than cut my rudder. I say leave the rudder alone.

I most certainly won't argue with that!

[geoleo]

Dont have much choice in this as its not 'anchoring' but the only dock around. as I stated first off-------------" a strong & long east wind blew all the high water out of all the bays & -intracoastal waters in the Tampa bay area about 18 months ago--------- people were walking on the bay bottom in downtown Tampa- thats when rudder bottom got roughed up....... news said this was a very rare 80 year thing that had not been seen in memory. At least the keels wing was not damaged or the rudders bearings and such. Im just trying to get a little more clearance Insurance. (4"more + aluminum plate).

[coopec43]

"As Hurricane Ian made its way toward Florida on Wednesday, it appeared water had receded from Tampa Bay, as if the body of water had been drained and dried out. The phenomenon, called a blowout tide or a reverse storm surge, is an indicator that a hurricane is on its way." 28 Sept 2022

https://www.cbsnews.com/news/hurrica...stal-flooding/

[geoleo]

Have decided to not put any metal plate on bottom of rudder. Aluminum would be bad choice anyway. LOL! Just going to cut off 4" and couple layers FG matt with 1" radius edges.

[MicHughV]

You really should be using sail trim to balance your boat, not rudder trim, so 3" chopped from the rudder is hardly bound to make a noticeable difference.

From a purely mathematical point of view, pressure increases the deeper down in the water column you go, so while it is only 3" of rudder missing, the lower portion of the rudder is in the densest water.

Skipping ahead, have you seen the rudders on the latest batch of AC75 boats, they are the thinnest of blades, mind you, those boats are travelling at 30 knots.

At the end of the day, how much will that 3" matter to a boat moving at 5-6 knots. I'm off the opinion...not much, considering how much area of the rudder remains.

Off course, it could be mathematical determined, but why ??

[boatpoker]

Originally Posted by geoleo

Have decided to not put any metal plate on bottom of rudder. Aluminum would be bad choice anyway. LOL! Just going to cut off 4" and couple layers FG matt with 1" radius edges.

Matt is the weakest type of glass, typically used as a skinout or for non-structural parts, never used for strength. Should not be used with epoxy. Epoxy should be used in this application as polyester has a much weaker secondary bond.

[BenBowSirocco]

Originally Posted by geoleo

Have decided to not put any metal plate on bottom of rudder. Aluminum would be bad choice anyway. LOL! Just going to cut off 4" and couple layers FG matt with 1" radius edges.

I disagree, Aluminum is a great material for this application.

Use thickened epoxy as your glue. Shape your plate to your rudder and router the edge over. Grind the back of your plate bright with 65 grit, apply unthickened epoxy to your plate and sand it with some 40 grit by hand while wet: this will help you achieve a very good bond. Screw it or clamp it into place and remove the screws after its cured.



If you do use glass instead, as others have stated, dont use Chopped Strand Matt. I would use a pre-fabricated fiberglass plate from an industrial supplier.



That type of plate is usually made under several tons of pressure and will be far denser than anything you make without vacuum bagging.

[Jim Cate]

From a purely mathematical point of view, pressure increases the deeper down in the water column you go, so while it is only 3" of rudder missing, the lower portion of the rudder is in the densest water.

Ummm.... Water, being essentially non-compressible will have no density change in the water column at a depth of a few feet.

And I doubt that the OP will ever notice the difference in steering performance or balance.

Jim

[Kettlewell]

This thread is a good example of why sailboats should be able to take the ground safely. You would think cats would be great in this regard, but wandering around the boatyard this spring I was surprised by how many modern cats have spade rudders that hang way down and have obviously already contacted the bottom at some point. Personally, I don't think any sailboat should have a rudder that doesn't draw at least a foot less than the keel if it doesn't raise or kick up.

[CarlF]

Originally Posted by geoleo

Have decided to not put any metal plate on bottom of rudder. Aluminum would be bad choice anyway. LOL! Just going to cut off 4" and couple layers FG matt with 1" radius edges.

It would be very easy to dig out about 1/2" of the foam and put in a piece of 1" G10 (save money by laminating a few thinner pieces together). The G10 should stand proud of the rudder, roughly follows the rudder profile and have your radius edge. Apply a good thick bead of epoxy stuctural filler around the sides and over the top and trowel smooth. After hardening, sand well t and then applly 3 or 4 layers of biaxial tape in epoxy resin overlapping 6" on the rudder sides.

[Lee Jerry]

Originally Posted by geoleo

Im considering cutting 3-4 inches off the huge rudder so it has a little more clearance as in such situations above. . Boat has great rudder control and I dont think it will affect sailing ability. Comments please.

Originally Posted by geoleo

rudder is about 50 inches long 4 inches off would be losing 8%+ bottom is banged up and needs repairing anyway. Boat steers exceptionally well in all conditions so Im gambling that 8% area loss wont hurt steering. Actually its less than 8% as rudder tapers smaller at bottom.

You're helped by the fact that this is a long spade rudder set way back from the keel. I have trouble believing that you'll notice 3" missing.

You really should be using sail trim to balance your boat, not rudder trim, so 3" chopped from the rudder is hardly bound to make a noticeable difference.

At the end of the day, how much will that 3" matter to a boat moving at 5-6 knots. I'm off the opinion...not much, considering how much area of the rudder remains.

And I doubt that the OP will ever notice the difference in steering performance or balance.

Planform area is only one factor in the rudder performance. Another is aspect ratio - higher is better, and you are proposing lowering it. So you will not only have a smaller rudder (in area), but also a less efficient one (in shape).

Consider it this way...
For any given situation, such as sailing at whatever wind speed and angle, the boat needs a given steering force. The required rudder angle with the shortened rudder will be higher than with the original rudder. Therefore, the drag will be higher and boat speed lower.

[MicHughV]

Jim,
If you were to consider a dam wall, the pressure of the water against the dam wall will be the greatest at the toe of the wall.

[geoleo]

Originally Posted by boatpoker

Matt is the weakest type of glass, typically used as a skinout or for non-structural parts, never used for strength. Should not be used with epoxy. Epoxy should be used in this application as polyester has a much weaker secondary bond.

I meant Woven Roving. Maybe tapes of approximately size needed to kind of fit. Potential problem is bending roving 90 degrees up sides. Help--lol

[Matt Johnson]

Originally Posted by geoleo

I meant Woven Roving. Maybe tapes of approximately size needed to kind of fit. Potential problem is bending roving 90 degrees up sides. Help--lol

You want +45/-45 Double Bias fiberglass. 12oz (about 450gm) does well bending around curves without much distortion, but a more readily available is 1708 which is a 17oz DB with mat attached.