Spinning In vs Spinning Out

[Rayzor]

For everyone that wants to know why spinning in vs spinning out causes different forces on the transom, it is all because of the angle of deadrise on the sponsons. When spinning in, there are less degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way up, than down - which equals more force generated pulling the prop down (causing bow lift). The reverse is true when spinning out, there are more degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way down, than up - which equals more force generated pushing the prop up (causing stern lift).

[quicklt1]

just for clarification,,, this is in ???
292395

[Double Rigged]

No out

[Rayzor]

The drawing is just to show the difference in height from the bottom of the prop to the surface of the water as it relates to the bottom of the sponsons. The props are entering water that is at the same angle as the bottom of the boat, not flat. At the speeds the boats are running and as close as the props are to the transom, the water doesn't have time to flatten out at all.

[eli]

if i would boat at night i would have to install some of them lights those are cool .

[Onetime]

For everyone that wants to know why spinning in vs spinning out causes different forces on the transom, it is all because of the angle of deadrise on the sponsons. When spinning in, there are less degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way up, than down - which equals more force generated pulling the prop down (causing bow lift). The reverse is true when spinning out, there are more degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way down, than up - which equals more force generated pushing the prop up (causing stern lift).



Interesting and I'll have to think on it a bit.

One comment. Your sketch shows the props not being in the tunnel at all. What does it do, with this line of thinking, when the props are inboard more and catching the air from the tunnel?

You probably can't mount any closer to the tunnel with your Arneson Drives and maybe not with a Mercruiser drive either.

Pretty sure my 24 had the props catching air from the tunnel. Can't look at my 28 right now to see.

[quicklt1]

This is in

[CaptainCraiger]

http://i314.photobucket.com/albums/ll434/FreezeFrameVideo/FreezeFrameVideo041/69.jpg (http://s314.photobucket.com/user/FreezeFrameVideo/media/FreezeFrameVideo041/69.jpg.html)What would be better on this rig, turn them in or out?

[CaptainCraiger]

Side view of the boat.http://i314.photobucket.com/albums/ll434/FreezeFrameVideo/FreezeFrameVideo040/55.jpg (http://s314.photobucket.com/user/FreezeFrameVideo/media/FreezeFrameVideo040/55.jpg.html)

[Superbender]

I must respectfully disagree with my friend rayzor spinning in as illustrated by quicklt1's second picture,will generate stern lift relying on the boats natural ability to carry the nose for a overall lift, rayzor is correct about the fact that spinning in looses bite.spinning them out will carry the nose better ,spinning in is not for everyone.now think about for a second the two props turning in push down causing stern lift,please note prop choice plays an important role in set up as well.

[RBT]

Wait till t2x see this, he has the best explanation I have read yet.

rt

[davemvegas]

on rayzors drawing it shows the whole prop behind sponson. I am close to drilling my transom for twins. at 58 1/2 prop shaft spacing I think the inside of props will be a few inches inside tunnel. I don't think I can get the motors apart far enough to place prop behind sponson. any better place to mount my motors then where I am about to mount them?292405 lisa told me to stay in the chair. she has this job covered. it is hard to see in the pic but 58 1/2 put the nose of sportmaster right behind the drain plug you can see on the left sponson.

[aaron78viper]

Side view of the boat.http://i314.photobucket.com/albums/ll434/FreezeFrameVideo/FreezeFrameVideo040/55.jpg (http://s314.photobucket.com/user/FreezeFrameVideo/media/FreezeFrameVideo040/55.jpg.html)

On that boat, depending on how far forward or back the fuel and the rest of the weight aboard will likely come into play. which is why the other thread had lots of people saying to try both. Im guessing with 4 huge motors hangin off the back, you want to turn them out(being its a rear heavy v bottom) which would lift the stern. BUT if the fuel is farther forward than expected, and the boat doesn't ever lift the bow, maybe the opposite. For many people, it might never matter at all. just my opinion.

[eli]

on rayzors drawing it shows the whole prop behind sponson. I am close to drilling my transom for twins. at 58 1/2 prop shaft spacing I think the inside of props will be a few inches inside tunnel. I don't think I can get the motors apart far enough to place prop behind sponson. any better place to mount my motors then where I am about to mount them?292405 lisa told me to stay in the chair. she has this job covered. it is hard to see in the pic but 58 1/2 put the nose of sportmaster right behind the drain plug you can see on the left sponson.
this is a 23 daytona might help little

[davemvegas]

on the 23 pic the motors appear to be just to outstde of sponson center. I think on my 22 the sponson is a little narrower. 58 1/2 spacing puts prop shaft to the inside of sponson center. should I go as wide apart as I can. to get as much of prop blade out of tunnel. and try to get most of the prop behind sponson? how low are your prop shafts below sponson? it looks to be a few inches or more in pic. I was thinking to mount at center and be able to adjust above or below sponson. from your pic it looks like I may need to mount motors a couple inches lower then I thought.

[Onetime]

For everyone that wants to know why spinning in vs spinning out causes different forces on the transom, it is all because of the angle of deadrise on the sponsons. When spinning in, there are less degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way up, than down - which equals more force generated pulling the prop down (causing bow lift). The reverse is true when spinning out, there are more degrees of rotation of the blades spinning down in the water than there are degrees of rotation spinning up in the water. Therefore, the blades are spending more time in the water on the way down, than up - which equals more force generated pushing the prop up (causing stern lift).

Dale,
I have to disagree with your statements. You are not giving any physics as to why it does or doesn't create stern or bow lift.
Your statements are refering to the amount of blade that is in or out of the air stream when the boat is running fast. These statements are pertinant to prop efficiency and the blade getting a cleaner bite of water as it enters the water. As I said in my previous post, what happens when the blade is partially in the tunnel and catching air from the tunnel? Does this reverse your theory because prop can get more air from the tunnel side?

What is your source for your statements and theory?

[davemvegas]

where should the nose of my gear case line up. is it better to try and get the whole prop behind sponson.292553 or let half of the prop in tunnel?

[Rayzor]

Dale,
I have to disagree with your statements. You are not giving any physics as to why it does or doesn't create stern or bow lift.
Your statements are refering to the amount of blade that is in or out of the air stream when the boat is running fast. These statements are pertinant to prop efficiency and the blade getting a cleaner bite of water as it enters the water. As I said in my previous post, what happens when the blade is partially in the tunnel and catching air from the tunnel? Does this reverse your theory because prop can get more air from the tunnel side?

What is your source for your statements and theory?

You can disagree with what I have posted Richard, as it doesn't matter to me. I take what I have learned from Peter Hledin, Howard Arneson, Rik Wimp and Rick Bowling over the past 15 years as fact. Not to mention the testing I have personally done on three different 28s I've owned, as well as my 30. If you can't understand the forces the blades are seeing as they spin through the water, than you probably won't understand what I'm trying to explain. I'm certain if you stop by my dock the next time you're out on the Delta, I could explain it to you while looking at the back of one of my boats when it's up out of the water.

[Rayzor]

where should the nose of my gear case line up. is it better to try and get the whole prop behind sponson.292553 or let half of the prop in tunnel?

I rigged my 23MTR so that the centerline of the motors was set so the gearcases were completely clear of the tunnel walls. From all of my research, I found that getting some of the prop diameter into the water flow coming through the tunnels was beneficial for performance, but you do not want to be dragging any of the gearcase through this water flow, as it will just create drag.

[davemvegas]

rayzor, thanks for your input. I ordered 2 12" slidemaster manual jack plates today. I guess I will play with the throttles and adding gauges while I am waiting for the slidemasters.

[Rayzor]

rayzor, thanks for your input. I ordered 2 12" slidemaster manual jack plates today. I guess I will play with the throttles and adding gauges while I am waiting for the slidemasters.

Good luck with your re-rig! It sounds like you are setting up your rig for smooth water running with that much setback. Slidemasters are the best manual jackplates though, IMO!

[eli]

they are above I can measure I looked over the back at 70 mph with someone driving and saw more than 1/2 of the prop out of the water neutral trim or slightly neg trim

[davemvegas]

Good luck with your re-rig! It sounds like you are setting up your rig for smooth water running with that much setback. Slidemasters are the best manual jackplates though, IMO!

there is no splash well or any opening on the back of my boat. it is about the same as mounting a motor to the side of a wall. it takes at minimum a 10" plate to keep the cowl off the transom. I went the extra 2" so I can trim the motors up a little.

[Davidlake]

Thanks Dale for taking the "mystery" out of the prop rotation issue. I am an architect that has a good handle on forces and your drawing/explanation puts the question to rest for me! I now also understand why different props make a hull react differently. Thanks to your thread on this, I will be better able to tune my new 28 Skater (if I ever get back from painting). Ha Ha. David

[quicklt1]

The going up on sponson scenario , makes sense for turning out to pull boat back down

[SUNKIST]

Ahh, gotta love the smell of two stroke oil in the morning293659spinning out

[Motv18]

The ones I see are set lhr on port rhr on starboard. When asked I get the safety speech. Prop torques the opposite back down. All ways wondered what kept it from just paddle wheeling away should it get bAd enough. Do you toe in or out spinning out to get the motors running straight under power.

[props4u2]

The ones I see are set lhr on port rhr on starboard. When asked I get the safety speech. Prop torques the opposite back down. All ways wondered what kept it from just paddle wheeling away should it get bAd enough. Do you toe in or out spinning out to get the motors running straight under power.


Toe out.

[props4u2]

I have personally always seen that turning the props in lifted the transom and out lifted the bow on V-hulls and cats.

Just my observation.

[Rayzor]

Thanks Dale for taking the "mystery" out of the prop rotation issue. I am an architect that has a good handle on forces and your drawing/explanation puts the question to rest for me! I now also understand why different props make a hull react differently. Thanks to your thread on this, I will be better able to tune my new 28 Skater (if I ever get back from painting). Ha Ha. David

Glad to hear my explanation makes sense to you David. It's sort of difficult to explain over the internet without any interaction with the guys trying to understand it. If you have any rigging questions with your 28, feel free to PM me. Between what I've learned on my own, recommendations from Pete over the years and the knowledge Rick Bowling has passed down to me (he's owned his 28 for over 15 years now!), I think I have a pretty good handle on different setups on these boats. Please post up pics when you get your 28 out of paint! Mine's also in the paint booth as we speak! - Dale

[SUNKIST]

http://www.screamandfly.com/attachment.php?attachmentid=292394&stc=1&thumb=1&d=1392510701 im sure someone can put this into a mathmatical formula showing the actual specific forces be applied. with all the input from peter and your other sources, how much tow out should be applied approximatly in this photo, specifically related to catamarans. appreciate the great drawing showing the physics behind it. obvioulsy there are several variables involved but in general applied to the back of my boat several post above.