interspersed ...

"otnmbrd" wrote in message
ink.net...

....


A simple test, would be both engines astern, equally. Since they are
both "left hand", your boat should immediately start backing to stbd.
How quickly and at what "turn rate", would indicate the degree of prop walk.
I'm guessing here, but I'm betting you can steer your boat astern by
just increasing/decreasing throttle on one or the other of the engines?


I don't recall the boat ever doing anything other then going straight back as it first
started up.

Yes, I back down a long narrow fairway with throttle alone, rudders centered.




Thus, the net affect is zero propwalk, but I have no way to determine whether the
individual engines are generating propwalk.

Another way would be back on port engine and get a sense of "turn rate",
then back on stbd and compare (backing on stbd, could/should produce a
slower turn rate)

Yes, I should try that, if only to get an answer to this question.




BTW, the builder claimed this was a non-issue, but when they started building larger
sailing cats, and the powercat, they used counter-rotating props, because it was an
option
with the larger transmissions.

Your transmission/reverse gear is only built to turn in one direction?
Can't be built to turn opposite?

No, obviously there is a reverse, but many transmissions favor one direction amd the
other is only for intermittant use. There are differences in the gearing and the
lubrication. Other transmissions can be set up either way. I don't know what the issue
is with the small Volvo and Yanmar saildrives but the only props they (Volvo) make for
them are LH - I take that as a sign.

There is an often talked about case of a trawler that was setup counter rotating by
running one tranny in reverse. It took them a while to figure out why that transmission
always cooked in a few hundred hours.




Overall, I'm guessing that the spacing of your props, andG as mooron
says, the fact you have folding props of relatively little "bollard
pull" means that for most maneuvers you do, prop walk will be there, but
not of enough significance, when compared to the reaction of your boat
to the spacing and thrust of your props, so, as the builders claim, it
will generally be a non issue.


maybe so, maybe so.

otn

G Also interspersed

Jeff Morris wrote:

A simple test, would be both engines astern, equally. Since they are
both "left hand", your boat should immediately start backing to stbd.
How quickly and at what "turn rate", would indicate the degree of prop walk.
I'm guessing here, but I'm betting you can steer your boat astern by
just increasing/decreasing throttle on one or the other of the engines?



I don't recall the boat ever doing anything other then going straight back as it first
started up.

Interesting, G another test for next year?

Yes, I back down a long narrow fairway with throttle alone, rudders centered.

Sounds like a twin screw with outboard turning props, although we know
this isn't the case.
Think we're learning some things about "cats" here ... have a feeling
it's mainly due to spacing/hull length.




Thus, the net affect is zero propwalk, but I have no way to determine whether the
individual engines are generating propwalk.

Another way would be back on port engine and get a sense of "turn rate",
then back on stbd and compare (backing on stbd, could/should produce a
slower turn rate)


Yes, I should try that, if only to get an answer to this question.




BTW, the builder claimed this was a non-issue, but when they started building larger
sailing cats, and the powercat, they used counter-rotating props, because it was an

option

with the larger transmissions.

Your transmission/reverse gear is only built to turn in one direction?
Can't be built to turn opposite?


No, obviously there is a reverse, but many transmissions favor one direction amd the
other is only for intermittant use. There are differences in the gearing and the
lubrication. Other transmissions can be set up either way. I don't know what the issue
is with the small Volvo and Yanmar saildrives but the only props they (Volvo) make for
them are LH - I take that as a sign.

I say transmission/reverse gear, purely to note different terms for the
same thing.
It's interesting to note they only make the "gear" for left hand
.....wonder why....

There is an often talked about case of a trawler that was setup counter rotating by
running one tranny in reverse. It took them a while to figure out why that transmission
always cooked in a few hundred hours.

Have run across this situation in the past. It's not normally a quick
presto - chango. Sometimes engines were and possibly still are, built to
run opposite, and I remember one Boston ferry, was built with engines
gears set up for inboard turning props ( shocked the hell out of the
operator, first time he maneuvered it, since it didn't react at all like
what he was used to or expecting). It was, I believe, done
inadvertently, and they ended up switching gears and props to outboard
turning.

otn




Overall, I'm guessing that the spacing of your props, andG as mooron
says, the fact you have folding props of relatively little "bollard
pull" means that for most maneuvers you do, prop walk will be there, but
not of enough significance, when compared to the reaction of your boat
to the spacing and thrust of your props, so, as the builders claim, it
will generally be a non issue.



maybe so, maybe so.


otn