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Search took 0.00 seconds. Search: Posts Made By: jwalker
Forum: Engines & props 14 March 2006, 17:51
Replies: 29
Views: 3,914
Posted By jwalker
Nope, you've got it right. You loose speed...

Nope, you've got it right. You loose speed because the pitch goes down but you gain speed because the engine revs higher. You are trying to get the best compromise to end up with the engine producing...
Forum: Engines & props 14 March 2006, 11:11
Replies: 29
Views: 3,914
Posted By jwalker
Andy, now you're into the realm of wishful...

Andy, now you're into the realm of wishful thinking. :)
Forum: Engines & props 14 March 2006, 00:23
Replies: 29
Views: 3,914
Posted By jwalker
It's easy enough to understand and your dad was...

It's easy enough to understand and your dad was correct except I don't know why it would need to be in a vacuum.

With your gear ratio of 1.87, your engine will turn 1.87 times more than your...
Forum: Engines & props 13 March 2006, 23:41
Replies: 29
Views: 3,914
Posted By jwalker
10% is pretty good and with an efficient hull I'm...

10% is pretty good and with an efficient hull I'm sure it's realistic at high speeds.

For a general purpose motor pushing a wee boat I'm guessing 20%ish.

My previous rib had about 15-18% at...
Forum: Engines & props 13 March 2006, 23:08
Replies: 29
Views: 3,914
Posted By jwalker
Well you've got to check rev counter cos if your...

Well you've got to check rev counter cos if your actually pulling higher revs, you may well get more speed with a higher pitch. You have to have accurate figures to do this stuff and my 20% is also...
Forum: Engines & props 13 March 2006, 23:00
Replies: 29
Views: 3,914
Posted By jwalker
Using your figures and 20%, it gives a boat speed...

Using your figures and 20%, it gives a boat speed of 24.5mph. If your GPS is accurate at 30mph, you must be pulling higher revs.
Forum: Engines & props 13 March 2006, 22:57
Replies: 29
Views: 3,914
Posted By jwalker
Still a problem with your figures cos at 1.85...

Still a problem with your figures cos at 1.85 you've got only about 3.4% prop slip. :)

I'd rough guess at about 20%.
Forum: Engines & props 13 March 2006, 22:52
Replies: 29
Views: 3,914
Posted By jwalker
The manual. That's it, then. You're at max...

The manual.

That's it, then. You're at max power as it is. End of story.
Forum: Engines & props 13 March 2006, 22:41
Replies: 29
Views: 3,914
Posted By jwalker
I don't think you can go faster. At least, not...

I don't think you can go faster. At least, not much. I can't remember what the max revs are for the 30 Yam but I'd guess at 5500. If that's a correct assumption, pitching down will gain you a couple...
Forum: Engines & props 13 March 2006, 22:23
Replies: 29
Views: 3,914
Posted By jwalker
You'll go slower.

You'll go slower.
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