89er

Sidecar

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Nice fence detail……

The clean “exhaust” for air coming out of the back of the boat, how much importance do you put on it? The rudder support assembly looks impossibly thin and fragile, (I am sure it is plenty strong enough) .

Contrary to that, I was amazed at how heavy (and smooth/faired in) the rudders supports assemblies were on the back of some 18 ft skiffs, until you remember that there is a fair chance that sooner or later, a couple of crew will fall off the racks and onto them, and the assembly has to take it all without unnecessarily maiming the crew in the process.
 

peterivanac

Member
318
15
Nice fence detail……

The clean “exhaust” for air coming out of the back of the boat, how much importance do you put on it? The rudder support assembly looks impossibly thin and fragile, (I am sure it is plenty strong enough) .

Contrary to that, I was amazed at how heavy (and smooth/faired in) the rudders supports assemblies were on the back of some 18 ft skiffs, until you remember that there is a fair chance that sooner or later, a couple of crew will fall off the racks and onto them, and the assembly has to take it all without unnecessarily maiming the crew in the process
Lol. I always appreciated the strong 18' skiff rudder gantry as a way to get back in the boat.
 

Sidecar

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Lol. I always appreciated the strong 18' skiff rudder gantry as a way to get back in the boat.
Another reason perhaps why they seemed to be so faired in and smooth.

Many years ago, I got thrown out of a Melges 24 when it broached and laid over with a kite up doing 19 knots. Upside down in the water, I reckoned it best to continue holding the mainsheet, and as the boat continued to flog and stagger along at around 6 knots, it turned me over, and I surfaced, body surfing behind the boat. Pulled myself back in over the stern, and we went on to win the race.
 
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JulianB

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On my AAMI's I did not have the rudder frame.

The only reason to have a rudder frame is to get the tiller another 300-400mm further back.
Everything else about them is bad.

They are heavy.
They take the Le of the rudder away from it's ideal position
They let the rudder ventilate easily.
They often require a bigger rudder.

It's all negative. It's all slow.
 

bushsailor

Anarchist
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not sure of the whole composite rigging tests but as a rule of thumb I use 6 times max load to size stays etc to stop it creeping. Then it will not stretch creep etc etc ever. Problem is then windage.
 

JulianB

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Lots of hydrofoil work today
1669444098126.png

The 400gm/m³ foam top gasket on the top of the fin that GT and I made on Wednesday, just prior to glassing. Front to M8 threads take a Carbon Plate, (2 photos down) that make a very positive stop to the board going down the case, but 99% will be down by the wedge angle of this top gasket.
1669444136245.png

Another angle of the top gasket.

1669444173609.png

The 6mm Carbon plate, with some M8 bolts positioning it.

1669444216912.png

And pretty happy with the bulb nearly the final paint job, you can see the "zebra" line from the reflection of the table in it, it's pretty fair, very happy with it.

Tomorrow, big day on the mast. My D24 sailing has been called off, pity, have wanted to sail one of those for years but the YC has changed the schedual, un-beknown to Rob.

Not short of things to do on the 89er, so a good thing in some ways!

jB
 

kprice

Member
185
2
SF Bay
Lots of hydrofoil work today
View attachment 555910
The 400gm/m³ foam top gasket on the top of the fin that GT and I made on Wednesday, just prior to glassing. Front to M8 threads take a Carbon Plate, (2 photos down) that make a very positive stop to the board going down the case, but 99% will be down by the wedge angle of this top gasket.
View attachment 555911
Another angle of the top gasket.

View attachment 555912
The 6mm Carbon plate, with some M8 bolts positioning it.

View attachment 555913
And pretty happy with the bulb nearly the final paint job, you can see the "zebra" line from the reflection of the table in it, it's pretty fair, very happy with it.

Tomorrow, big day on the mast. My D24 sailing has been called off, pity, have wanted to sail one of those for years but the YC has changed the schedual, un-beknown to Rob.

Not short of things to do on the 89er, so a good thing in some ways!

jB
JB, what is done at the bottom of the case to take the clearance out?
 

JulianB

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JB, what is done at the bottom of the case to take the clearance out?
GT lined the fin with about 0 5mm of mylar/tape, he did it quite accurately and then treated the fin with Era-release which is a silicon in suspension agent. Put it all in place, lined it up, then very careful and throughly damned it.
Normally I would use a urethane something around 85 (hardness of a soft skateboard wheel), but in this case I used epoxy. Just pour it down the TE. You do that so you get about a 80mm rise at the TE and about 50mm at the LE (unlikely to hit something hard going backwards) latter I will line the bottom (& top) 50mm with billard table felt which is about 0.75mm thick. That way, when you push it down, it compressthe felt and you get a good seal with about 0.25mm movement.
I will probably be there tomorrow and I will get a 📸, jb
 

JulianB

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What will you use to raise and lower the keel for trailering?
If we stay with the SKUD Bulb it's only 145-150kgs, so 4:1 or a 6:1 block and tackle on a strap around the boom. KISS!!
If we do Marley Point, or City - Surf, then a bit of U section alloy 300mm long, with a strap around at the LE can hold it up so the B&T is released and we get the boom back.
Just KISS
 

JulianB

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@JulianB I'm curious about the fence on the rudder. Is that similar to a deck sweeper arrangement on a sail for endplate? What is the purpose? Thanks
So I'm searching for my book by Curry, and I know Marchaj did it latter also. They put a series of peido tubes along the keel of a boat, and then X distance out from the CL to measure the pressure along the length of the hull. My friend Dina, she and her husband are NA's and work for the US set me a graph of a power boat at speed showing these same pressure differentials. So basically, you have a up-tick in pressure about ¼ of the way back from the bow, where the “breast” of the boat is, you then get a “relative” drop in pressure as you come further aft but then about 2” (50mm) infront of the transom you have another up-tick in pressure, no where as big as the one at the front but double or triple that 300”” fwd and very obviously significantly bigger than that 300mm behind the transom. And you can observe all of this, just by looking at the rooster tail or pressure (release) hump you get just after the transom. All the time remembering water is in-compressible.

So, if you can put the LE of the rudder, in a perfect world, just aft of this spike then you a) get accelerated flow across the LE of the rudder (nb1) and b) a continuation of the pressure gradient.

The issue of course is this spike in pressure moves fwd and aft dependant on speed, so if you angle the LE of the rudder aft and you put the very top part of the LE infront of this spike, and allow the rudder to taper back, then you get the best of both worlds.

As I have commented before, I expect to be able to reduce the size of the rudder 100-200mm, that has phenomenal consequences on top end speed, Ken Warby (Spirt of Australia) went from Zero (mid 200’s MPH) to Hero, World water speed record holder (316mph) by taking a angle grinder to the last 2” (50mm) of his rudder between the 2 runs. This happened in 1978, BTW, in the middle of Australia.

I do expect this boat to occasionally hit mid 20’s in boats speed, I expect that because I did sail Vivace down Lake Macquarie in about 2006 and we hit something like 25.6knts on during that race.

Plenty of experience in the size of the rudder and the placement of the LE in 18teens, and even if you look closely at a 49er, we attempt to get it as far FWD as we can, and a 49er rudder is tiny compare to that of say a I14 or a 5o5.

nb1, and this allows you to reduce the size of the rudder for the same output (turning capacity). You see this most vividly by the size (almost ½) of a rudder that is under a boat than one that is transom hung or worst gantry hung.
 

WCB

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So I'm searching for my book by Curry, and I know Marchaj did it latter also. They put a series of peido tubes along the keel of a boat, and then X distance out from the CL to measure the pressure along the length of the hull. My friend Dina, she and her husband are NA's and work for the US set me a graph of a power boat at speed showing these same pressure differentials. So basically, you have a up-tick in pressure about ¼ of the way back from the bow, where the “breast” of the boat is, you then get a “relative” drop in pressure as you come further aft but then about 2” (50mm) infront of the transom you have another up-tick in pressure, no where as big as the one at the front but double or triple that 300”” fwd and very obviously significantly bigger than that 300mm behind the transom. And you can observe all of this, just by looking at the rooster tail or pressure (release) hump you get just after the transom. All the time remembering water is in-compressible.

So, if you can put the LE of the rudder, in a perfect world, just aft of this spike then you a) get accelerated flow across the LE of the rudder (nb1) and b) a continuation of the pressure gradient.

The issue of course is this spike in pressure moves fwd and aft dependant on speed, so if you angle the LE of the rudder aft and you put the very top part of the LE infront of this spike, and allow the rudder to taper back, then you get the best of both worlds.

As I have commented before, I expect to be able to reduce the size of the rudder 100-200mm, that has phenomenal consequences on top end speed, Ken Warby (Spirt of Australia) went from Zero (mid 200’s MPH) to Hero, World water speed record holder (316mph) by taking a angle grinder to the last 2” (50mm) of his rudder between the 2 runs. This happened in 1978, BTW, in the middle of Australia.

I do expect this boat to occasionally hit mid 20’s in boats speed, I expect that because I did sail Vivace down Lake Macquarie in about 2006 and we hit something like 25.6knts on during that race.

Plenty of experience in the size of the rudder and the placement of the LE in 18teens, and even if you look closely at a 49er, we attempt to get it as far FWD as we can, and a 49er rudder is tiny compare to that of say a I14 or a 5o5.

nb1, and this allows you to reduce the size of the rudder for the same output (turning capacity). You see this most vividly by the size (almost ½) of a rudder that is under a boat than one that is transom hung or worst gantry hung.
Julian,

Thank you so much for an amazing answer! That makes complete sense and I'm no NA. Now you'll have me staring at my new 505 rudder that I have to lay up soon and is very deep. I'm almost tempted to play around with some changes to it.
 

JulianB

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WCB, Mp, I did find this, I think it's from Dina, in which case it's likely to be a patrol boat, so big deep vee, isoclinal shape. It's also plannig!

1669637208035.png


To wrap some numbers around it, and again this is a Deep Vee Planning boat, the front spike at the breast of the boat is around 40 psi, the back one is about 10 psi (sorry about the imperial measurements, it's Dina and she's Merican). The bit in the middle can get low as 1-2psi but never negative.

I am yet to find my Manfred Curry, from memory he did it very well, and the spikes associated with a HP sailing skiff (and this is Hamburg pre WW2, later Princeton ) were far more pronounced, far more "spiky".

I also think it explains the march aft of masts/rigs, because if you can put your fin/centerboard between 0.55 and 0.65, based on necking therory, you are far better off.

And again, this has to be tempered with the % time spent at planning speed and the time spent displacing. The presure distribution will be very different bow down at below HS than it will be nose up and sending it.

But the spike just prior to exiting the transom will always be there, regardless of speed or mode and it's a great place to put your LE.

I do remember a 18teen, pretty sure it was Rob Brown, probably just before Entrad, that had a rudder that went down in a box in the aft deck (which they had in those days) and the rudder was very small. Also the rudder on Skeeter (a 79er) is a similar arrangment, and small and they swear by it.

The AAMI/Nokia/Ella Bache, rudders of the 1990's where all exactly 1m (39" was the magic number), into the water when on the back of the boat with the LE underneath. They have been growing in length, as they have moved back, ever since, I think they are now up to about 1.3m, fat, etc etc.

The 1990 boats had (mostly) 17ft wings, but even with 21ft and the ridiculous 32 - 25ft winged monstors had this 39" depth when on the back of the boat (no rudder frame).

Not sure why we did not advocate going (completly) under the boat. I know we tried it and ruled it out. Maybe complexity, maybe finding this sweet spot nullified any additional benift.

BTW, I am no NA either, Dad said it was the best thing I ever did, switch from NA to ID.
I'm sure if the AMC existed then or I had gone to Southamption or Maine, it could have been different, but I went to Montreal with Ian (at Dad's insistance) and did ID!
 

Sidecar

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Not sure why we did not advocate going (completly) under the boat. I know we tried it and ruled it out. Maybe complexity, maybe finding this sweet spot nullified any additional benift.
Surely it has to do with the distance between the foil and the rudder?

Too small a distance and you need bigger rudders. Double the distance between, and you halve the rudder load, which means you can have smaller rudders. Don’t ask me how I know.

A rudder completely under the boat, if designed right, is endplated, which increases its effectiveness, and potentially leads to a further reduction of rudder area and drag.

Your fence detail at least endplates the leading edge.
 

Jethrow

Super Anarchist
I couldn't find a decent photo (the one below was the best) but when watching the 18'ers on YouTube you often see quite a large rostertail between the trailing edge of the hull and leading edge of the rudder. I assumed that little endplate tucked and faired into the hull was to quieten that down...
1669664489993.png


Edit: and then this photo shows up in my Facebook feed to show what I mean!
1669665485618.png
 
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Sidecar

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The fence will obviously help with any disturbance at the top of the rudder as well. Free flowing water hitting a vertical leading edge will always cause some vertical wash/spray.

The other thing that isn’t so obvious is that the rudder, with ~ 60 mm of it forward of the pivot, is at least partially balanced. One rule of thumb is ~ 17%. If 60mm is 17%, then that is good for a rudder with a chord of~350mm. And at 35mm max thickness, that’s 10%, pretty good for a rudder.

The fence disc has been sized to give endplate to the front third of the rudder, where most of the lift is generated.

All in all a very neat bit of rudder design.

9E7D4470-BE07-4993-89A2-6109E2E5B4A4.png


PS:

Julian, one question, why brass tube bushing?
 
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Varan

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Knowing zero about this, my naive guess about the plate would be it was to prevent air getting sucked down and ventilating the rudder. Boy was I wrong. Must have tubercles brain disease.
 

JulianB

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Why Brass, used it for years, super thin wall so you can maximise reinforcment.
It's not as if the rudder is doing 360 RMP, and its inert and it dose not graunch.
Basically because it's idiot proof!

The fence, DOSE inhibit ventalation, so you rnot wrong.
But far more importantly it allows you to put the LE of the rudder were it should be.
I used a 135mm Dia disc, because that was the size of my ginders disc, and that makes making the recess amazingly simple (probably some imperial (5 1/4") std)

You can all have what ever theroy you wish to have, that's all your preogative, I have found that sticking the LE at point X has worked, so I am doing that. If you have found putting it point Y works for you, all power to you, go your hardest, but you have not convinced me to change course.

And 17% is VERY balanced, I like about 13%, and if I fine tune the tip, and may have to fine tune the balance which is very easy adding material to the TE,

~~~~~~~~~~~~~~~~~~~~~

Today, I had hope to stand the mast, it did not happen, (so no photos) the sicaflex did not stick the Titanium button nuts, so early start tomorrow, with GT to try and get back on track.

Probably won't beer can race tomorrow, I will work on the boat to get back on track!

jB
 




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