shrouded propeller v.s nonshrouded opeller

[matty87]

not entirly sure how old this thread is but i noticed a couple of posts up that a few surf life saving links were up about the effectiveness of these guards. it may be so that these guards have no real safety advantage to offer on very high speed craft when someone is hit at full tilt but as a member of the surflifesaving in australia i can assure you having been hit by these prop guards a number of times in training in rough seas that i went home very sore but with no cuts which i would have had if no gaurd was in place. the gaurds also protect the propelor from constantly running into the ground as the craft is beached. just a different point of view.

[yipster]

was reading up on CFD and came acros this bladeless is more article
checked http://www.dyson.com/fans/ and the video's
nobody stuck such an expensive fan upside down under water
couse we all know drag would be terrible rite ?

[jehardiman]

Originally Posted by yipster

was reading up on CFD and came acros this bladeless is more article
checked http://www.dyson.com/fans/ and the video's
nobody stuck such an expensive fan upside down under water
couse we all know drag would be terrible rite ?

Venturi Pump design, very lossy with water.

[tom28571]

Bladeless fan. Cute but not worth a second look. On a cost to performance ratio it fits in with the Amish Edenpure heater and airconditioners.

[yipster]

rite, apart from the impellor and all i recalled a waterjet only works well above above the surface, remains a nice expensive fan tho

[PAR]

Tom, you're being overly kind to the latest invention from sir Dyson. I heard one running at a Lowe's not long ago. I went to the trouble of turning all the other running fans off and it was loud all by itself and the air movement wasn't particularly impressive. Yep, it had no blades (well visible anyway) and interestingly enough it sounded like an Electrolux with a bad beater bar . . .

[MooringProJeffL]

I have built a work barge with twin 50hp outboards and was considering shrouded props for better direction of thrust. There were several interesting points brought up in the discussions.
A shroud designed to improve thrust most likely will not provide any reasonable protection of body parts at slow speeds. At high speeds you are going to be injured with just the impact.
Having owned one of the first jet skis made and worked on them a lot. The clearance between the impeller and the shroud is measured in a few thousands of an inch. Run this jet ski up on the beach, suck in some sand, open the clearance by .01" and you will lose the hole shot and 5mph.
The shroud on an outboard propeller will create cavitation problems at higher speeds and the package is less efficient.
For better info on propellers ask Larry at I have built a work barge with twin 50hp outboards and was considering shrouded props for better direction of thrust. There were several interesting points brought up in the discussions.
A shroud designed to improve thrust most likely will not provide any reasonable protection of body parts at slow speeds. At high speeds you are going to be injured with just the impact.
Having owned one of the first jet skis made and worked on them a lot. The clearance between the impeller and the shroud is measured in a few thousands of an inch. Run this jet ski up on the beach, suck in some sand, open the clearance by .01" and you will lose the hole shot and 5mph.
The shroud on an outboard propeller will create cavitation problems at higher speeds and the package is less efficient.
For better info on propellers ask Larry at http://www.accutechmarine.com/


Jeff Lefebvre
www.New-England-Marine.com
New-England-Marine LLC
1429 East Lakeshore Drive
Colchester, Vermont 05446

[SamSam]

Originally Posted by MooringProJeffL

I have built a work barge

I'd like to hear a little about that.?

[MooringProJeffL]

There is a lot of info and pictures of me work barge at this link.
http://www.newenglandmooring.com/con...g-work-barge-m

The props are more for thrust than speed. Top speed is 12mph forward and 5mph in reverse. Each motor has independant throttle and steering. Yes, two steering wheels and they are not so hard to operate. Handling is superb and it can turn quickly rotating on its center.
Even with the low pitch props, idle speed is 2mph. Too fast for trolling.
I will install four blade props next season for more thrust. The 30" diameter pontoons are rated for 115hp each.

[SamSam]

Thanks!

[Willallison]

I'm a little surprised that the findings against Brunswick haven't been given more attention around these and other parts. It would be interesting to hear what Brunswicks lawyers are telling the company as a result... there was talk that it could result in ALL new outboards and sterndrives being fitted with safety shrouds, which would likely have a very significant effect on the performance / efficiency of the boats to which they are fitted.
And since it happened in the country where personal responsibility appears to have been banned, I can't imagine that they would consider that it's worth the risk of hoping that they won't get sued again....