Does propslip make you go faster?
03-10-2003, 08:13 PM
#12
Registered
Thread Starter
Join Date: Feb 2002
Location: Lake Michigan
Posts: 6,627
Likes: 0
Received 0 Likes
on
0 Posts
Hmmm...rv I got it.
The higher the x dim. the less drag/drive in the water and then the more your prop vents itself out or slips.
Thus loosing speed because of the slip...so to compensate, pitch is increased and its all good with the top speed thing again.
But i would guess having more of that pitch and just being at a cruise speed you would loose throttle responce and the boat will seem sluggish.
With my 10-11% slip my boat has tremedous throttle responce and feels very fast, or very powerful in the seat of the pants.
The higher the x dim. the less drag/drive in the water and then the more your prop vents itself out or slips.
Thus loosing speed because of the slip...so to compensate, pitch is increased and its all good with the top speed thing again.
But i would guess having more of that pitch and just being at a cruise speed you would loose throttle responce and the boat will seem sluggish.
With my 10-11% slip my boat has tremedous throttle responce and feels very fast, or very powerful in the seat of the pants.
Last edited by Back4More; 03-10-2003 at 11:06 PM.
03-10-2003, 08:13 PM
#13
Registered
Where is Tomcat when we need him......
we were trying to find efficiency curves for props ( thrust vs slip)
don't seem to be in the public domain.
I wonder. in the extreme case...... what do the big cats with surface drives have for prop slip. that should tell you about how to set a surface piercing prop up. and a high x dimension conventional drive might be somewhere between the approximate 15% optimal for a submerged prop and what they run on surface piercing setups.
we were trying to find efficiency curves for props ( thrust vs slip)
don't seem to be in the public domain.
I wonder. in the extreme case...... what do the big cats with surface drives have for prop slip. that should tell you about how to set a surface piercing prop up. and a high x dimension conventional drive might be somewhere between the approximate 15% optimal for a submerged prop and what they run on surface piercing setups.
03-10-2003, 08:22 PM
#15
Registered
exactly back....
Tomcat and I were trying to apply BEA (basic engineering analysis) to save time and $$$ and determine the optimal prop for a given boat and power configuration.
we can't seem to find any curves on particular props, but it seems the few generic curves by mercury racing show the peak thrust around 15% slip for submersed props
so who has a dialed in surface drive boat, and what speed, rpm drive ratio and pitch do you have.....
Tomcat and I were trying to apply BEA (basic engineering analysis) to save time and $$$ and determine the optimal prop for a given boat and power configuration.
we can't seem to find any curves on particular props, but it seems the few generic curves by mercury racing show the peak thrust around 15% slip for submersed props
so who has a dialed in surface drive boat, and what speed, rpm drive ratio and pitch do you have.....
03-10-2003, 09:57 PM
#16
An excellent question. I think it is worthy of following up on. Maybe one of you could call Team Archer, Arneson, or Pulse Drive and get the answer.
As for the ventilated hull problem, I can imagine a situation where a ventilated hull might let the prop slip more, but (due to less resistance in the water) have the boat go faster.
I think conventional hulls vs ventilated hulls vs surface drives might be apples vs oranges vs melons. Dunno.
I like MELONS, myself.
As for the ventilated hull problem, I can imagine a situation where a ventilated hull might let the prop slip more, but (due to less resistance in the water) have the boat go faster.
I think conventional hulls vs ventilated hulls vs surface drives might be apples vs oranges vs melons. Dunno.
I like MELONS, myself.
03-11-2003, 07:28 PM
#17
Registered
um.......kaamascarab, do you not have kaama surface drives??????
what props, drive ratios. rpm, and speed you runnin
what props, drive ratios. rpm, and speed you runnin
Last edited by Rambunctious; 03-11-2003 at 07:32 PM.
03-11-2003, 07:47 PM
#18
Platinum Member
Platinum Member
My #3 Speedy drives aren't true "surface drives" , but the prop shafts are about 1" above the bottom.
At the engines turning 5,900 (they will turn more) and drive ratio of 1.5-1 + props 17.5 x 35 4 blade Merc Labs with a lot of cup (have to calculate them as 36"). Speed is 121.9 on GPS.
Every hull has different requirements and needs. With my setup the slip is about 9%.
Diameter is the key on my boat. But you can't swing that diameter on either a Bravo or Outboard.
At the engines turning 5,900 (they will turn more) and drive ratio of 1.5-1 + props 17.5 x 35 4 blade Merc Labs with a lot of cup (have to calculate them as 36"). Speed is 121.9 on GPS.
Every hull has different requirements and needs. With my setup the slip is about 9%.
Diameter is the key on my boat. But you can't swing that diameter on either a Bravo or Outboard.
03-12-2003, 07:25 AM
#19
Registered
Most of the posts here are thoughtful. There is no "magic" slip number. It is not a coincidence that there is a close correlation of of diameter/pitch ratio. If you use one of the examples above, and just increase the diameter, the "efficiency" (lack of slip) will increase like crazy, but the speed and rpm will surely go down. I like Wette Vette's analogy.
03-12-2003, 07:55 AM
#20
Platinum Member
Platinum Member
The main thing to remember is that you can't apply one setup to all hulls. Some of the Skaters (& other new cats) are running only 4-5% slip (maybe less). The diameter was recommended for my hull by Dennis C. at Merc Lab; he was correct.
