rudder alignment Q

[jfm]

One of our past suppliers (who had built many fast boats in his time) said toe in requirement was dependant on speed so a variable toe in linked to speed was the best solution. The faster it goes the more the rudders toe in.

In practice I'd go for parrallel and see how the boat behaves.

Sleipner/Side-Power are actually writing the software code now to have variable stabilser fin toe-in, dependent on speed. Each boat would be set up in the way Latestarter describes (except it would be done electronically not mechanically) and the stab computer will memorise the free flow position at each speed in say 2kt increments. Then it will adjust the toe-in on the stab blades according to boat speed. This was actually suggested 3 months ago by ellesar in another thread, which Sleipner read at the time and are acting upon! (The power of this forum!)

 

[MapisM]

The water flow isn't purely axial along the hull, becuase the V of the hull splays the water out sideways a bit.

Mmmm... I accept that for fins, but for rudders? Right behind the props thrust? Naaah...

 

[jfm]

Mmmm... I accept that for fins, but for rudders? Right behind the props thrust? Naaah...

I wouldn't argue with you strongly on this becuase I have no science/data so am just posting by the seat of my pants. But I wouldn't think the flow of water from the props can fully eliminate the sideways flow component caused by the V hull splaying the water though, and anyway see last para of Latestarter's post #16

 

[Latestarter1]

I wouldn't argue with you strongly on this becuase I have no science/data so am just posting by the seat of my pants. But I wouldn't think the flow of water from the props can fully eliminate the sideways flow component caused by the V hull splaying the water though, and anyway see last para of Latestarter's post #16

Probably on completely different context. However I can remember discussing laminar flow off V bottoms with Charles Currey another Fairey Marine man and pal of Uffa Fox. Charles was Commander of flotilla of MTB's dropping of agents off on French coast during the war. Those young guys were real smart, they understood exactly how laminar flow was outward from keel. They needed to know. German radar ws pretty basic and MTB's clustered together represent very small single target.

These guys knew exactly how to position their craft in order to use the laminar flow to keep vessels apart, get it wrong and they ended up being sucked together and possibly damaged with risk of being left behind when **** hit the fan.

 

[MrB]

I may be barking up the wrong tree but wouldn't "toeing in" your rudders cause unnecessary drag ?

 

[vas]

Have you completed the purchase of the boat V? In which case, congratualtions! Sorry if I missed the thread on this - the last I read (grey tanks), you had not completed yet.

well, err, I'm writting and rewritting the private docs to be exchanged between the seller and myself (don't ask, very worried, scared and fussy seller, but no worries) so version 3 left my computer 10 mins ago.

As soon as I get rid of the 20K euro cash I'm carrying in my pockets all day I'd consider the sale done. Hopefully tomorrow before lunch, so I could accept early congratulations, thanks!

I'll then update and close officially the original thread, many more threads to come full of questions and photos of the rebuilt over the winter, no doubt.

V.

 

[vas]

Up to a point I was following this thread nicely assuming that toe in means that the rear side of the rudders is pointing inwards (option A).
Now after jfm and others final contributions, it seems that toe-in means that rear of the rudders is pointing outwards (so front of the rudders is toed in so to speak) as the wake is created on the sides of the hull.
i.e. port rudder alone would turn craft to port, and sbrd rudder alone turn to sbrd.

So, did I get it right this time? (fwiw, mine are on option A atm)

cheers

V.

 

[MapisM]

it seems that toe-in means that rear of the rudders is pointing outwards (so front of the rudders is toed in so to speak)

Correct. At least, that's the way I've always heard of it in those cases (outdrives, as I said above, and actually also outboards) where I've heard of that. It makes sense to use the same logic also for rudders, I suppose.
Anyway, the fact that in your boat they're currently toed-out (assuming that nobody messed with them) is the best proof that there's no strict rule on this.
In your boots, I'd follow LS1 suggestion to find out the most neutral position empirically.

 

[MapisM]

I wouldn't argue with you strongly on this becuase I have no science/data so am just posting by the seat of my pants. But I wouldn't think the flow of water from the props can fully eliminate the sideways flow component caused by the V hull splaying the water though, and anyway see last para of Latestarter's post #16

Admittedly, I'm also posting on the basis of the same criteria, so I would neither put my right arm on what I told previously, nor on what I'm going to say now...
Otoh, following the same reasoning, I actually would expect the water flow behind the props not only to eliminate the V hull component, but to actually create (on average) an opposite effect.
In fact, within the overall water flow pushed backward by the props, there are obviously multiple components going in all trasversal directions at 360°.
But since the lower half of the prop is more effective than the upper half, on average the flow moving inward (towards the keel) is bound to be higher than the opposite flow. Just think of the rooster tail shape: it's clear that the water flow goes from the sides towards the center, not the other way round...

 

[jfm]

Yup, could be right, I see your logic. I really dont know!

To V, yes "option A" is "toe out"!