"Tuning" props for salt vs. fresh water.

When I worked for Circus Circus in the mid eighties I had the opportunity to work with Bill Bennett's unlimited Hydrofoil team "Miss Circus Circus" for two seasons as a telemetry technician and the race team did have sets of cleaver props that were pitched and tuned for water density's i.e. Salt vs Fresh. They were always dealing in fractions of speed increases but I can't see a motor yacht or S/F going to these extreme's. I'm sure if you drill down enough on the web there's going to be some viable information in regard to this topic and how it would apply to yachts.

I believe your talking about the spectacular double flip by the then two side by side Hydro's Miss Madison & Miss Circus Circus in San Diego 1988 ? I think that piece of video received more air time on ESPN and in the previews of any unlimited race after that. Bill Muncy threw in the towel after that experience. I don't want to get to far off topic of the thread but if your interested I have some stories of the egos and $$ involved between all those teams. Drivers, Crew chiefs and designers jobs were never safe and you lasted only as long as you won. Mr. Bennett was an interesting gentleman and I got involved with the Unlimited team after completing the build of his De Vries 42 meter Feadship in '83 / I'm told that a PM is now a conversation? still exploring the new site...

Different props for fresh or salt, not usually. However, the boat will sit lower in fresh water and also not be quite as fast. So if you're overpropped for Salt water, you'll be even more overpropped in freshwater.

On a huckins I ran we had fresh and salt props .helped with her speed as she floated differently

I'll usually see a yacht sit about an 1" lower on the water line than in salt water. I have noticed most 20+ knot yachts will lose about a knot in freshwater at cruise.

Yes, but with the shallow water you get some lift running so you don't notice it.....if you really look at the waterline, it's easy to tell, but you're losing weight as you go across......(fuel)

Left you a message

If the boat is in displacement mode in shallow water the draft will increase due to "squat." It will also require more power to achieve the same speed.

Both of those factors so far outweigh any difference due to water density effect on a small boat as to make the whole issue moot - in shallow water at least.

By running, I meant on plane. On Plane in shallow water you tend to gain a little speed. It is true with displacement speed that you will lose a little speed in shallow water, also they will handle very weird in shallow water and like to make 60 degree turns sometimes without any predictability.

That is called "bank effect" and is also related to bottom profile. While the extent is not very predictable, the effect is to be expected. I see it has not been mentioned yet but I suspect that may be one of the underlying causes of the recent Suez Canal collision.

No, if it gets shallow on one side of the hull at displacement speeds, the propellor on the shallow side will have a tendancy sometimes to suck the whole boat towards that side.....

Lots of good info around, here is a site with plain language information.

http://thenauticalsite.com/NauticalNotes/Manouev/MyMan-Lesson02-SHandling.htm