Prop reference point

Airboat propeller discussion.
Post Reply
Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Prop reference point

Post by Hotdog » Mon Jun 18, 2018 7:58 pm

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

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2832
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Prop reference point

Post by SWAMPHUNTER45 » Mon Jun 18, 2018 9:23 pm

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.

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Mon Jun 18, 2018 9:39 pm

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

User avatar
Prototype
Southern Airboat Member
Posts: 770
Joined: Sat Jan 26, 2013 2:28 pm

Re: Prop reference point

Post by Prototype » Mon Jun 18, 2018 10:02 pm

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!

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Mon Jun 18, 2018 10:16 pm

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.

never enuff
Southern Airboat Member
Posts: 104
Joined: Wed Mar 25, 2009 8:31 pm
Location: Ft.Pierce

Re: Prop reference point

Post by never enuff » Tue Jun 19, 2018 12:12 pm

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

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Tue Jun 19, 2018 12:41 pm

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

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Sun Jul 22, 2018 8:58 pm

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.

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 675
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: Prop reference point

Post by Slidin Gator » Sun Jul 22, 2018 10:39 pm

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.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

User avatar
Deano
Site Supporter - V
Site Supporter - V
Posts: 4549
Joined: Thu Jan 06, 2005 11:16 am
Location: Inverness, FL

Re: Prop reference point

Post by Deano » Mon Jul 23, 2018 7:45 am

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.
viewtopic.php?f=85&t=28600&p=276720
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Mon Jul 23, 2018 8:29 am

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

User avatar
Deano
Site Supporter - V
Site Supporter - V
Posts: 4549
Joined: Thu Jan 06, 2005 11:16 am
Location: Inverness, FL

Re: Prop reference point

Post by Deano » Mon Jul 23, 2018 8:40 am

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.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

SeatCover
Southern Airboat Member
Posts: 67
Joined: Mon Nov 06, 2017 7:33 am

Re: Prop reference point

Post by SeatCover » Mon Jul 23, 2018 8:49 am

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
12' Cut Gilleo, Angle Valve 0-320, 72" Whisper Tip. Goes wherever I point it. :florida:

Hotdog
Southern Airboat Member
Posts: 51
Joined: Mon Nov 27, 2017 6:31 pm

Re: Prop reference point

Post by Hotdog » Mon Jul 23, 2018 12:33 pm

There is no way to adjust the front mounts. I bent the back lip down about foot and half wide and still hops bad.

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 675
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: Prop reference point

Post by Slidin Gator » Mon Jul 23, 2018 1:56 pm

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!
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

User avatar
keebo
Site Supporter - IV
Site Supporter - IV
Posts: 1204
Joined: Wed Dec 26, 2007 8:48 pm
Location: Fort Pierce, Florida

Re: Prop reference point

Post by keebo » Mon Jul 23, 2018 2:28 pm

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.
Sure you can Trust our government, just ask an Indian


:old_glory: :florida: :GA:

User avatar
OneBFC
Southern Airboat Member
Posts: 616
Joined: Tue Sep 11, 2012 1:04 am

Re: Prop reference point

Post by OneBFC » Mon Jul 23, 2018 3:08 pm

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!
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

SeatCover
Southern Airboat Member
Posts: 67
Joined: Mon Nov 06, 2017 7:33 am

Re: Prop reference point

Post by SeatCover » Mon Jul 23, 2018 3:14 pm

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.
12' Cut Gilleo, Angle Valve 0-320, 72" Whisper Tip. Goes wherever I point it. :florida:

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 675
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: Prop reference point

Post by Slidin Gator » Mon Jul 23, 2018 6:13 pm

Following OneBFC's lead:

viewtopic.php?f=85&t=40298&p=389721&hil ... im#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.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

Post Reply

Return to “Prop Talk”