PDA

View Full Version : Can a prop give bow lift???



RiverToysJas
01-14-2003, 07:12 PM
My "cab-forward" style open bow has a CG that doesn't allow it to fully get back on the delta pad and air out the hull (at least with my big ass in the driver's seat). The fairly aggressive steps on my hull help a lot but I'd like to break water a little further back, if I can.
I've heard of some props help with bow lift. Is that true? Are there props that could help get more of my hull out of the water?
I'm happy with my performance, but would be willing to play around and see if there's a better prop for my situation.
I'm running a 22" Bravo 4-blade right now. After 20hours, I'll probably be switching up to a 24" Bravo 4-blade and also trying a few other props. I'm sure most of you know, but it's a Lavey Craft 21' XTSki with a 496Mag.
Thanks for any suggestions you guys may have.
RTJas :D
[ January 14, 2003, 07:22 PM: Message edited by: RiverToysJas ]

rivercrazy
01-14-2003, 07:31 PM
I'm a newby along with Jason so I have some of the same questions. What I've read in a few places is generally speaking, a 4 blade gives you more stern left and a 3 blade more bow lift. Is this on the right track?

playdeep
01-14-2003, 07:50 PM
RTJ,
call Bob Teague and see if he has any NOS Mach patriots left.
For 200.oo bucks it makes for a good speed run,spare prop.
I used to run them on my last two 25 Eliminator eagle's.They were the hot ticket before merc came out with the bravo1 series.
The only down side is that they have a propensity to pitch a blade after a while.

Havasu Hangin'
01-14-2003, 08:06 PM
Yeah...what those guys said.
3 blades are usually faster on the top end. I'd try a 3 blade 23" or 25" for a top-end prop.
I know a prop guy if you wanna try some out.
[ January 15, 2003, 03:39 AM: Message edited by: Havasu Hangin' ]

77charger
01-14-2003, 08:35 PM
A good thumb on the trim button,An extra shot of nos :) ,a good wake,get the fat chicks to the back of the boat eek! ,ghost driving(you sit in the back), :cool: a droop snoot(oh i forgot you dont have a jet no more) :) ,let me drive it for you since i weigh 90 pounds wet, :D , And maybe a three blade prop.

RiverToysJas
01-14-2003, 08:42 PM
77charger:
A...get the fat chicks to the back of the boat eek! ...The only thing that's fat on the chicks in my boat is their attitude! wink
RTJas :D

Infomaniac
01-14-2003, 08:47 PM
I still have my Blueprinted Quicksilver Mirage 3 blade 27p. What an awesome prop. Would fly the nose of my 21' Seebold pad V. Takes a lot of rake for bow lift.

RiverToysJas
01-14-2003, 08:49 PM
Infomaniac:
Takes a lot of rake for bow lift. Rake in the shape of the prop?
RTJas :D

77charger
01-14-2003, 08:52 PM
What is rake?would that be in the angle of the blades? :confused:

Havasu Hangin'
01-14-2003, 08:55 PM
RiverToysJas:
Rake in the shape of the prop?Rake is how far the ears are set back...past the end of the hub creates a twisting..

Infomaniac
01-14-2003, 08:56 PM
Yes Rake is The tip of the blade point aft. Hard to describe.
If you were to draw a line from the tip of the blade to the hub, the farther back it is angled, the more rake the prop has.

Infomaniac
01-14-2003, 09:02 PM
Dave Rycroft worked that prop over for me. It was not even close to the same prop when he was finished with it. The blades were about half the original thickness and razor sharp on the leading edges. He left a ridge on the trailing edge. The water stops (slows) momentarily before it goes off the blade. Causes the prop to bite like crazy.
A B&M blown small block turned that 27 pitch prop 5,200 RPM with a 1.36 ratio Alpha SS.

Havasu Hangin'
01-14-2003, 09:03 PM
Infomaniac:
Yes Rake is The tip of the blade point aft. Hard to describe.
If you were to draw a line from the tip of the blade to the hub, the farther back it is angled, the more rake the prop has. Yeah...what he said.
Most 4 blades have smaller blades, so they do not extend past the end of the hub...
Infomaniac:
He left a ridge on the trailing edge."cupping" also creates lift...
[ January 15, 2003, 03:40 AM: Message edited by: Havasu Hangin' ]

77charger
01-14-2003, 09:21 PM
Infomaniac:
A B&M blown small block turned that 27 pitch prop 5,200 RPM with a 1.36 ratio Alpha SS. out of curiousity how how long did the drive last?

Trash
01-14-2003, 09:24 PM
I was waiting for someone to jump in with rake info. Blade shape and rake influence bow lift the most. RTJs, I've got a Mach Patriot you could try but unfortunately not enough pitch for your application unless you went with 1.36 gears. And that's not too economical....
You know, props are one of these half science/ half art things, and with all the boat tests, I'm wondering why there isn't a master database created to really pound out some emperical data. It would be a heck of a lot easier when it comes to prop selection time. It would need to consider more than just pitch and diameter too. Blade shape, rake, thickness, sweep, x-dimension, blade surface area etc. need to be included.

rivercrazy
01-14-2003, 10:17 PM
Keep this info coming!

gnarley
01-14-2003, 10:55 PM
It would be nice to see everyone post REAL MPH, HP, RPM, ratios, hull type, weight, Prop size, type prop, work done to them by whom, & what they did to the actual ride. This could start some collective type input for a database to share in helping everyone with prop selections based on real world testing!
Maybe Hot Boat would compile the list for all forum members who would share the info & make it available for us to see??? It would make life a bit easier sharing real info knowing what to expect from someone else’s hard earned knowledge.

Infomaniac
01-15-2003, 05:18 AM
We'll have some good data in a month or 2. I am building a 10-71 blown 540 for "Well Done". It will go in his 23' Wyatt tunnel. Built here in Oklahoma. Going to see if it is possible to get this thing to 120.

Infomaniac
01-15-2003, 05:20 AM
77charger:
Infomaniac:
A B&M blown small block turned that 27 pitch prop 5,200 RPM with a 1.36 ratio Alpha SS. out of curiousity how how long did the drive last? I ran it for 8 years and as far as I know it is still going. Not the same power inm front of it. An Alpha SS is fairly stout. No wide open starts helps.

Hermosa
01-15-2003, 07:39 AM
gnarley:
It would be nice to see everyone post REAL MPH, HP, RPM, ratios, hull type, weight, Prop size, type prop, work done to them by whom, & what they did to the actual ride. This could start some collective type input for a database to share in helping everyone with prop selections based on real world testing!
Maybe Hot Boat would compile the list for all forum members who would share the info & make it available for us to see??? It would make life a bit easier sharing real info knowing what to expect from someone else’s hard earned knowledge. Stingray boats did something like that, they tested each boat, motor package and prop with real world test results, so you can get a good idea of how your boat will preform before you order the setup. I'm sure it took them some time and money for all tht extensive testing, I would love to see other manufacturers do that, especially the custom boat companies. You pay a lot for the boat, give us some good data and testing also. It wouldn't be that hard to call all their new boat owners a year after the get their boat and see what props have been working for them and in what application. A little R&D would be nice...

gnarley
01-15-2003, 08:25 AM
Hermosa, does Stingray have that info available for the general public to see?

steve@kps
01-15-2003, 10:13 AM
Are there any "prop" guys on here?
props, are like engines, there are too many combinations to just say "this is what you need".
There are props w/ certain blade designs and # of blades to get close to a good setup for a customer. Then the fine "tuning" is done to really bring a prop into specs and get the most out of the horsepower from the engine,outdrive,hull type, etc. Forget the old theory, 3 blades are faster than 4 blades, that is just NOT TRUE in all cases!
This is certain to be long thread and hopefully some really good reading for all to enjoy. :)
an easy way to describe "rake" .
Pitch is the actual angle of the blade from the leading to the trailing edge. Rake is the opposite angle, from the tip to the barrell, being the heighth of the tip in relationship to where the blade attaches to the barrell. (lay your hand flat on the table, then pull up your fingers towards the palm, and twist the hand, that's what rake is.) eek!
[ January 15, 2003, 10:36 AM: Message edited by: steve@kps ]

rivercrazy
01-15-2003, 10:31 AM
I've gone to OSO a few times and there seems to be some prop guru's over there from time to time.
www.offshoreonly.com (http://www.offshoreonly.com)
Maybe we can encourage some of those peeps to come over and post here. It usually pretty quiet in the outdrive section here on hot boat

Infomaniac
01-15-2003, 10:36 AM
steve@kps:
Are there any "prop" guys on here?
:) Yea You

steve@kps
01-15-2003, 11:04 AM
LOL, i just don't want to step on any toes. know what i mean. I hate to interfere in others territory. I respect anyone w/ enough balls to get into the prop business, it's very tough, and very expensive.

spectras only
01-15-2003, 01:29 PM
[QUOTE]Originally posted by gnarley:
Hermosa, does Stingray have that info available for the general public to see?, Gnarley, I remember the article mentioned by Hermosa. I think it was in HB .I'll try to go through my mags this weekend and will post it if I find it.

gnarley
01-15-2003, 10:28 PM
Attila, that would be great if you find it. Stingray made some hulls very similar to mine so I could get some useful info from that. I'm just about to start the winter work, pull the drive & transom adapter off & re-gel from the rub rail down, after I can do some serious prop testing. I might even install a nose cone while its apart to help reduce the drag. The current prop 14 ½ X 28 3 blade Raker produces to much bow lift and porpoises & is a bit slow to plane so I think a 4 blade cleaver would do the trick but I didn't want to waste money on a prop before I do all the work & then spend it again.

steve@kps
01-16-2003, 07:51 AM
gnarley,
You have the right idea in switching props. Too much "rake" creates too much bow lift and will seriously effect the holeshot. too much rake will also cause a boat to turn to the left and scare the crap out of ya at higher speeds.
pitch at the correct rpm's to create horsepower is where the speed is at!

twistedpair
01-16-2003, 11:27 AM
There was a pretty good thread on this @ HavasuBarney, you might want to check out this link:
web page (http://www.havasubarney.com/cgi-bin/ikonboard.pl?s=3e2703080944ffff;act=ST;f=25;t=2)

gnarley
01-16-2003, 11:42 AM
Steve since you are one of the resident experts would you mind if I sent you some questions by email? Or if everyone wants to learn & you answer them here I can do that also, or even a concensus from others who have been-there-&-done that.

SchellSchock
01-16-2003, 11:49 AM
Props....so many choices and way to much conflicting infor....
What I did was take mine, (F8 DuoProps) to the pros and told em what I was trying to accomplish. Wa-La better top end, same hole shot etc. (4 mph improvement. RiverToysJas...keep in mine that changing the size and or pitch just might get you what you are looking for. I know that the mpf difference on my boat changed the running attitude and moved the wetted surfaced back quite a bit.
Just my $.02

steve@kps
01-16-2003, 02:06 PM
gnarley, i don't mind answering or "helping" w/ any questions. I can only speak from my expierences. I just hate conflict. My ideas may be different from someone elses. There are many different things to do to props, and everyone seems to think there way is the only way. I say bull shit, correct a problem w/ the blades and put the rpms where they need to be and work the blades to create the correct amount of lift and wa-lah, you have a great running boat. I just don't want to be considered as the only person that knows what to do to everyones boat.
Your more than welcome to e-mail directly or ask for my opinion here. Or at bassboatcentral.com under the props forum.
Ya'll be cool. :D
[ January 16, 2003, 02:11 PM: Message edited by: steve@kps ]

SchellSchock
01-16-2003, 04:10 PM
Here is some good info from Popular Mechanics
web page (http://popularmechanics.com/outdoors/boating/1997/9/Comparison_Boat_Props/index.phtml)

gnarley
01-16-2003, 04:55 PM
SchellSchock, to bad that comparison didn't use the same diameter props of different styles to really see what could happen. Is it fair to compare a 13 3/4 x 21 to a 14 3/4 x 23??? I don't think so, but this showed more of what the different designs could do without explaining what those design differences were.
Steve you have email.
[ January 16, 2003, 04:58 PM: Message edited by: gnarley ]

Kim Hanson
01-16-2003, 06:52 PM
I know that mine isn't an I/O, but I run this 14.5/30 pitch merc chopper.I was told on HavasuBarney that chopper's are bow lifter's and cleaver's are stern lifter's....( . )( . ).... wink http://free.***boat.net/ubb/Avatars/Forum_Graphic_Depot/30-pitch.JPG

Infomaniac
01-16-2003, 06:57 PM
Kim you need to raise that engine about 6 inches. Maybe more
[ January 16, 2003, 06:58 PM: Message edited by: Infomaniac ]

RiverToysJas
01-16-2003, 07:09 PM
SchellSchock:
RiverToysJas...keep in mine that changing the size and or pitch just might get you what you are looking for. I know that the mpf difference on my boat changed the running attitude and moved the wetted surfaced back quite a bit.
Thanks, I'll probably start by seeing what happens when I go up to the 24" prop.
Lots of great info in here, I'm glad I asked!!!
Thanks guys, RTJas :D

steve@kps
01-17-2003, 07:18 AM
Kim, that's one BAD ASS ride!
your right on the blade performance description. If you tried to run a cleaver style prop on that boat, i doubt you'd be able to turn the wheel. Plus, it would probably chinewalk severly.
VERY cool boat, have a great summer!

SchellSchock
01-17-2003, 12:49 PM
gnarley
SchellSchock, to bad that comparison didn't use the same diameter props of different styles to really see what could happen. Is it fair to compare a 13 3/4 x 21 to a 14 3/4 x 23??? I don't think so, but this showed more of what the different designs could do without explaining what those design differences were.
I agree thought this was a decent starting place though. If you do a search for "props" there is like 200 items returned so tons of info.

Ian
01-17-2003, 02:44 PM
I know my boat is probably much slower than most of yours, but I think it performs well for what I got. It's an 87 Bahner with a 265HP 350 and an Alpha 1 running a 23 pitch Quicksilver SS 3 blade. With two people and about twenty gallons of gas it runs 60MPH at about 4800 rpm's, it also planes real quickly, it doesn't porpose at all, but it does seem to chine a little.
http://free.***boat.net/ubb/Avatars/Reader_Rides/Stern_Drives/106-0604_IMG.JPG
[ January 17, 2003, 02:46 PM: Message edited by: Ian ]

gnarley
01-17-2003, 03:22 PM
Ian, Whats the pitch on that screw? Has it been worked on at all? Any cupping? What's the drive ratio?

RiverToysJas
01-17-2003, 05:29 PM
Ian:
...With two people and about twenty gallons of gas it runs 60MPH at about 4800 rpm's, ...Is that GPS speed?

Ian
01-17-2003, 05:52 PM
Yes it is GPS, I'm not sure what gears are in the outdrive and I don't belieive the prop has ever been to the shop

Well Done
01-17-2003, 06:05 PM
Ian,
You have a nice looking boat. I know a few fellow boaters who would like to have one like yours.

Ian
01-17-2003, 06:12 PM
Well you know what they say, everythings for sale. wink I wouldn't mind getting into an older Daytona.

Kim Hanson
01-17-2003, 06:30 PM
Infomaniac:
Kim you need to raise that engine about 6 inches. Maybe more My jackplate does that Info,I can raise it alot .......( . )( . )..... :D

Havasu Hangin'
01-17-2003, 06:39 PM
Kim Hanson:
My jackplate does that Info,I can raise it alot .......( . )( . )..... :D I'm gonna go out on a limb and say that you'll pick up at least 3MPH without that tie-down wrapped around the lower case, too...

Kim Hanson
01-17-2003, 07:35 PM
Your funny HH,I was setting the timing on it and didn't need to take off the hold down strap.Notice the nice plug's,all 3 where left at home and the best I could come up with was my T-shirt.lmao....( . )( . )..... http://free.***boat.net/ubb/Avatars/Forum_Graphic_Depot/30-pitch.JPG
[ January 17, 2003, 07:36 PM: Message edited by: Kim Hanson ]

mike37
01-17-2003, 07:41 PM
steve@kps
Id like to know what prop works best on your HTM
like to know the best one for my boat
how is it going are you close to finishing it

Havasu Hangin'
01-17-2003, 07:43 PM
Kim Hanson:
Notice the nice plug's,all 3 where left at home and the best I could come up with was my T-shirt...Whew...you were scaring me for a minute, there Kim...
I was gonna tell ya that it's probably not a good idea to run around with paper towels for plugs!
Glad you got it under control... http://www.planetsmilies.com/smilies/happy/happy06.gif

Infomaniac
01-17-2003, 08:03 PM
mike37:
steve@kps
Id like to know what prop works best on your HTM
like to know the best one for my boat
how is it going are you close to finishing it Any beach resistant prop will work.

mike37
01-17-2003, 08:25 PM
Infomaniac:
mike37:
steve@kps
Id like to know what prop works best on your HTM
like to know the best one for my boat
how is it going are you close to finishing it Any beach resistant prop will work. probly need tree resistant bow with one of those props

steve@kps
01-20-2003, 02:34 PM
Hey, Mike37.
HTM is still jacking around, i haven't recieved any parts yet. Lia e-mailed the other day saying they are waiting for the attorney's...... some day i'll get to take it to the lake.
I've made many calculations and talked to Powertech (our prop mfg.). We are going to start w/ a stock 28p 4 bl. OFX. this is a 15.25 diameter w/ 23deg. of rake and an exteme amount of tip cup! estimations show at 5600rpms and 90% effecient we'll be at 89mph. that's w/ a 1.50 gear ratio. After we feel confident w/ the boat, i'm sure i can do some tweeking and sharpening on the blades and bring down the slip percentage around 5-7%. this hull should be a very effecient hull.. Our horsepower is figured at 510hp. It's 454 w/ a b&m 250 megablower (no internal specs avail.)
My experiences are that with these heavy boats a 4blade prop will be more effecient than the 3blades and will handle much better. Remember, i'm trying to lift the stern, not the bow. the 4 blade will help me do that.

SchellSchock
01-21-2003, 05:09 PM
What steve@kps said.....
Not I've made many calculations and talked to Powertech (our prop mfg.). ... But... Hey, where'd i set my BEER? LMAO

mike37
01-21-2003, 05:13 PM
SchellSchock:
What steve@kps said.....
Not I've made many calculations and talked to Powertech (our prop mfg.). ... But... Hey, where'd i set my BEER? LMAO so SchellSchock
give me you .02 on the best prop

gnarley
01-24-2003, 09:54 AM
Hey everyone I was just curious if any of you had any numbers to contribute here about prop slip, HP, weight & MPH?
http://free.***boat.net/ubb/ultimatebb.php?ubb=get_topic;f=6;t=000309

SchellSchock
01-24-2003, 10:54 AM
Mike37.
All humor aside my suggestion would be to take advice offered from this thread and bounce that against advice from a prop manfacture or a prop re-builder. I use The Propeller Shop and Pacific Marine Propellers here in San Diego and they have never steered me wrong.

gnarley
01-24-2003, 11:35 AM
Don't want advice, I want real numbers from real people who know what their real HP, weight, MPH & prop slip are with a given combo to see what the different combinations yield, which might produce a realistic assessment of what is happening & what someone could expect to see with varying degrees of the combinations.

tbisme
02-02-2003, 07:18 AM
I don't know if this will help but if you know tru-info about your combo, you can use this for a starting point then try to get a prop shop to tweek it out for you. It's pretty good for playing around w/ theroy.
speed calculator (http://www.go-fast.com/boat_speed_predictions.htm) :p

gnarley
02-02-2003, 10:34 AM
Thanks for the suggestion, I know about mine & am about to switch props based on info from my baseline. I am just really curious about what others with I/O's get for MPH from their hull, drive, blade, RPM & HP. The more info I have the better I can make changes in the future based on shared data that I am happy to put in as well.