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Prop reference point

Posted: Mon Jun 18, 2018 7:58 pm
by Hotdog
Hey all, just rebuilt my boat and trying to set the pitch on my prop. I have a 13' db, 4 seat set up top driver and pass seats with seat box. 434ci 650hp with a 2.37 rotator and a 76" 3 blade R series sensinich. On the blades there are 1 2 and 3 marks. Just wandering what a good starting point would be for overall performance. Any advice would be appreciated

Re: Prop reference point

Posted: Mon Jun 18, 2018 9:23 pm
by SWAMPHUNTER45
Normally if you don't have any prior experience with the blades you would start at the 2 mark was the way I was taught.

That's a lot of engine for 3 76' blades make sure you watch that tach and don't over spin the blades or engine.

Re: Prop reference point

Posted: Mon Jun 18, 2018 9:39 pm
by Hotdog
It's what was on the boat and new or bigger blades are not in the budget at this time. I was thinking they were small so should start at 3 but still new at this so just looking for opinions

Re: Prop reference point

Posted: Mon Jun 18, 2018 10:02 pm
by Prototype
I'd say it's more around the 400 mark with those short 76 incher's.
600 you should be in the four blade 82 set around 2.99 needing another blade!

Re: Prop reference point

Posted: Mon Jun 18, 2018 10:16 pm
by Hotdog
I def agree on needing bigger blades or even 4 blades. Just trying to use what I have for the summer. The rebuilt def went over budget so trying to just run the boat and have fun for now.

Re: Prop reference point

Posted: Tue Jun 19, 2018 12:12 pm
by never enuff
My old setup 434 with 2.37 gear 80 in 3 blade r. ran the best choked to 58 ish for push and all around your going to have to choke the shit out of the 76 es

Re: Prop reference point

Posted: Tue Jun 19, 2018 12:41 pm
by Hotdog
Ya I will have to look into going bigger over the winter but for now I'll just watch the tach. No reason to turn high rpms. Not racing. Just crusing with the family

Re: Prop reference point

Posted: Sun Jul 22, 2018 8:58 pm
by Hotdog
Hey SA, hope everyone has been getting some riding in and dodging the rain. I got my boat up and running pretty good but I have a real bad hop in it. What reference does the motor have to be to the bottom of the boat. Are they both suppose to zero degrees to each other or another words parallel It hops if it's just me in the boat or if there is 2 people up front.

Re: Prop reference point

Posted: Sun Jul 22, 2018 10:39 pm
by Slidin Gator
Trim your motor and prop to point down to push the nose down and reduce hop. Adjustments are usually a washer at a time. Too much hop is bad all around, but pushing too much on the nose for better deep water running decreases dry ground capability.

Re: Prop reference point

Posted: Mon Jul 23, 2018 7:45 am
by Deano
Sliding Gator is spot on. Sounds like it may be a little high in the back.

The second post in this thread expands on motor trim adjustments.
According to Hoyle, would be a straight & true bottom with no hooks, rockers or dents.
https://southernairboat.com/phpBB3/viewtopic.php?f=85&t=28600&p=276720

Re: Prop reference point

Posted: Mon Jul 23, 2018 8:29 am
by Hotdog
I have solid plastic type spacers under the gear box now, I will try to find some that are smaller. I believe they are about 1/2" now so I will try to find 3/8" spacers

Re: Prop reference point

Posted: Mon Jul 23, 2018 8:40 am
by Deano
I have no way knowing how your front mounts are constructed, but it may be easier to add a washer under the front mount(s)?
For practical purposes, that may be an easier method to attain the same desired end.
I've done this a couple times in the past, and it works just as well if all the other parameters allow it as an option.

Re: Prop reference point

Posted: Mon Jul 23, 2018 8:49 am
by SeatCover
Also try working the back lip on the boat or maybe shimming the polymer in the back if you can't get the hop out with the motor angle. My boat hops no matter, trim tab and all, but runs the hill no problem because it's got a lot of rocker in the hull. Can pull the hull around with one finger when it's on wet grass. I run quick slick bottom...for now

Re: Prop reference point

Posted: Mon Jul 23, 2018 12:33 pm
by Hotdog
There is no way to adjust the front mounts. I bent the back lip down about foot and half wide and still hops bad.

Re: Prop reference point

Posted: Mon Jul 23, 2018 1:56 pm
by Slidin Gator
This conversation has me thinking about a power trim unit for the motor mounts vs. a trim tab. No hazard of hitting dry ground with the ice break engaged. Raise the front of the motor to push the nose down for deep water, lower the motor for dry ground.

Now I will never get my work done this afternoon!

Re: Prop reference point

Posted: Mon Jul 23, 2018 2:28 pm
by keebo
Had a friend who did just that on his 540 boat, had a cylinder built inplace of the rear mount that had 4 inches of travel, 2 up and 2 down.
He got sick and never got to try it out, pretty cool idea though.

Re: Prop reference point

Posted: Mon Jul 23, 2018 3:08 pm
by OneBFC
ZoomZoom (Bud), did this years ago on his 13B rotary powered boat. He is still around I believe. Smart and talented guy. makes his own hulls and concentric gear boxes too.

might be able to PM him for any lessons he learned before digging into your own version to save some time.




Slidin Gator wrote:This conversation has me thinking about a power trim unit for the motor mounts vs. a trim tab. No hazard of hitting dry ground with the ice break engaged. Raise the front of the motor to push the nose down for deep water, lower the motor for dry ground.

Now I will never get my work done this afternoon!

Re: Prop reference point

Posted: Mon Jul 23, 2018 3:14 pm
by SeatCover
I have a real heavy duty electric acme screws jack with just a few inches of travel, its light too. I may try this out and see how it goes. Makes me wonder why the adjustable "wing" behind the prop never took off, I always thought that could help a boat a lot while running ground but maybe just not enough time in it to make a benefit.

Re: Prop reference point

Posted: Mon Jul 23, 2018 6:13 pm
by Slidin Gator
Following OneBFC's lead:

https://southernairboat.com/phpBB3/viewtopic.php?f=85&t=40298&p=389721&hilit=motor+trim#p389559

Wild Bill wrote:here's pics of Zoom Zooms. I figured with all the reading on SA I have done regarding running dry best if the hull porpoises and other opinions that they run dry on certain material if they ride on the nose and varying load conditions and such that engine trim wouldn't be such a bad idea. Zoom Zoom's here looks REAL simple. I have 2 poly bushings one of each that will be mounted at the Rotator mount holes and a electric linear actuator very similar to a Lenco trim tab mounted at the front of the engine. Weel see.. . Image

Image


I don't see myself doing this anytime soon, but it's a cool idea. I'm trimmed free for ground and my hull hops around 35-40, which is a good indication to me to slow down any way.