Fat bottomed girls

[bil56]

on a wide stern boat, the double rudder is almost obligatory, the hull is very distorted and part of the rudder is out of the water ...

[Whokickamoocow]

Originally Posted by bil56

on a wide stern boat, the double rudder is almost obligatory, the hull is very distorted and part of the rudder is out of the water ...

Yep, its pretty normal to float the windward rudder. They are short by comparison to a single rudder as they don't need the extended draft to counter any heel.

[fc59]

Originally Posted by bil56

on a wide stern boat, the double rudder is almost obligatory, the hull is very distorted and part of the rudder is out of the water ...

Seems that Italia 11.98, X4³ mkII, or GS 44 do have rather wide transom, are single rudder, and do not have a very distorded hull ...

And are even good to very good sailboats ...

[MicHughV]

I wonder about the twin rudders though.
The immersed rudder is doing all the work, but the windward rudder is semi in the air, semi in the water, often at an angle...drag ????

[Dieseldude]

Both rudders are at the same angle, so angular considerations are the same. The windward rudder, being partially submerged presents less drag. If the submerged rudder's strength and hydrodynamics are sufficient to maintain steerage, what would be the problem? Perhaps in a rough sea, the windward rudder would take some sudden sea forces, causing control problems. Sudden forces are a shock load, so the rudders and linkages would need to be strong enough. But even a single rudder system is subject to variable forces of seas.

[zeehag]

there are wide bottomed girls and fat bottomed girls.the formosas are fat bottom girls and production boats of today are wide bottom girls.. is strange seeing fbg used on a wide bottom girl.

[mabowers]

Originally Posted by zeehag

there are wide bottomed girls and fat bottomed girls.the formosas are fat bottom girls and production boats of today are wide bottom girls.. is strange seeing fbg used on a wide bottom girl.

Can't resist...

"I got an old fat boat, she's slow but handsome,
Hard in the chine and soft in the transom.
I love her well; she must love me,
But I think it's only for my money." - Gordon Bok, Old Fat Boat

[Rucksta]

Originally Posted by MicHughV

I wonder about the twin rudders though.
The immersed rudder is doing all the work, but the windward rudder is semi in the air, semi in the water, often at an angle...drag ????

Drag yes
Lift /righting moment yes
Optimising Lift Drag ratio is an essential part of sailing

[zeehag]

Originally Posted by mabowers

Can't resist...

"I got an old fat boat, she's slow but handsome,
Hard in the chine and soft in the transom.
I love her well; she must love me,
But I think it's only for my money." - Gordon Bok, Old Fat Boat

\i know mine loves me for my money yes.. good song.

[Dieseldude]

Originally Posted by Dieseldude

Both rudders are at the same angle, so angular considerations are the same. The windward rudder, being partially submerged presents less drag. If the submerged rudder's strength and hydrodynamics are sufficient to maintain steerage, what would be the problem? Perhaps in a rough sea, the windward rudder would take some sudden sea forces, causing control problems. Sudden forces are a shock load, so the rudders and linkages would need to be strong enough. But even a single rudder system is subject to variable forces of seas.

Sorry, I think I missed your point. Yes, the windward rudder would be presenting drag on its partially submerged portion without much benefit of steerage that it would otherwise provide if submerged. Could be pure drag with no steering hydrodynamics. It would be a variable load as seas roll past. Not sure how significant this would be. But could make handling a bit erratic.

[DeValency]

Originally Posted by zeehag

there are wide bottomed girls and fat bottomed girls.the formosas are fat bottom girls and production boats of today are wide bottom girls.. is strange seeing fbg used on a wide bottom girl.

Yes, but there are design prices paid for it. Either deepen the bottom at the aft behind the keel - adding more drag - this isn’t done in the above boats. And/or:
Longer/deeper spade single rudder to compensate for the loss of steering water flow while healing (with flat bottom) - way more vulnerable!

HR already have five models with dual rudders and they seem to do very well. And HR definitely know something in serious offshore cruisers.

They even offer three rudders - special order only once every year on April 1st 🙂

[Whokickamoocow]

Originally Posted by Dieseldude

Sorry, I think I missed your point. Yes, the windward rudder would be presenting drag on its partially submerged portion without much benefit of steerage that it would otherwise provide if submerged. Could be pure drag with no steering hydrodynamics. It would be a variable load as seas roll past. Not sure how significant this would be. But could make handling a bit erratic.

Hi Diesel,
I can attest that I have never felt the boat or even the helm move from wave action against the rudder. You might get an occasional wave slap against the rudder face which you can hear but with no effect on the helm. It's a keel boat not a sports boat.
If I'm solo and its light airs you ignore the helm, you steer the boat with the sheets/traveller, not the rudder. Waves could hit the rudder all day, the helm doesn't move nor does the boat change in attitude. If you turn on the autopilot, you find yourself periodically checking to make sure its engaged because as long as your trim is right it hardly moves.

[Whokickamoocow]

Originally Posted by MicHughV

I wonder about the twin rudders though.
The immersed rudder is doing all the work, but the windward rudder is semi in the air, semi in the water, often at an angle...drag ????

Hullo Mic,
The windward rudder contributes a lot to helm response until the wind picks up enough to continually fly the windward rudder. The rudders are canted at about 15 degrees so I agree on paper it doesn't look efficient.
But if you sit on the transom and watch the rudder wakes, you can watch the effect in real time as the rudder rises and falls back into the water. You don't see any drag ie: vortices or turbulence, the wake trail just appears and disappears. If you didn't set your toe in (alignment) correctly then drag would be an issue , but that's the same for a single rudder boat.
You can fine trim the boat looking at the rudder wakes, its an easy way to spot any trim issues. You can see the wake trail from the windward rudder in this clip. This is a beam reach with us doing everything trying to induce some heel, watch how much I'm having to move the helm.
Cheers!

https://youtu.be/wfpNh5r1VyI

Edit: sorry , I dont know how to embed the video

[Dieseldude]

Originally Posted by Whokickamoocow

Hi Diesel,
I can attest that I have never felt the boat or even the helm move from wave action against the rudder. You might get an occasional wave slap against the rudder face which you can hear but with no effect on the helm. It's a keel boat not a sports boat.
If I'm solo and its light airs you ignore the helm, you steer the boat with the sheets/traveller, not the rudder. Waves could hit the rudder all day, the helm doesn't move nor does the boat change in attitude. If you turn on the autopilot, you find yourself periodically checking to make sure its engaged because as long as your trim is right it hardly moves.

Great that there are no issues with seas knocking the high and dry rudder. A deeper draft keel certainly helps to stabilize heading.

[Whokickamoocow]

Originally Posted by Dieseldude

Great that there are no issues with seas knocking the high and dry rudder. A deeper draft keel certainly helps to stabilize heading.

Yep, agree. Draft, ballast/displacement ratio and sail plan balance are all important parts of the boat having good manners.