Yet Another Prop Question....

[kirkland]

Okay i'm sorry for doing this to you guys but i don't know how else to assure myself that all i've read here has sunk in and i'm strarting to gain enough knowledge to be dangerous...<br /><br />17' Cajun bass boat<br />1991 70hp Rude<br />13 1/4 X 17 aluminum (OMC)<br />with 2 adults, full fuel, three batteries, 250 lbs other<br />i'm turning 5800 rpms..about 7 seconds to plane 38 mph(fishfinder) gps not onboard this trip..<br /><br />now same load out execpt 3 adults and 2 teenage boys about 5700 RPM and 36.5 MPH<br /><br />the Question i think i know the answer to is. Should i stay with the 13 1/4 X 17 and find a ss prop that has this spec, or will a OMC SST 13 3/4 X 17 be fine.<br /><br />also can someone tell me what my slip is..??<br /><br />Thanks

 

[Dhadley]

Re: Yet Another Prop Question....

Somethings a tad off. Those numbers show you at about 3% slip which is a bit too good to be true. But lets assume theyre close. The question is, if you go to a ss prop are you planning on dialing in the set up or are you strictly going to leave the motor where it is?

 

[kirkland]

Re: Yet Another Prop Question....

Not sure what i really need to do at this point.. again the speed is from the fish finder not GPS so i think the data may be off some....<br />The A/V plate is about 1 3/4 inches above the bottom of the hull... i've removed the dolphin that was on the motor and I don't see any reason yet to put it back on.. it was on the 50hp Johnny i had on the boat before and when motors were switched so was the dolphin...<br />I have room to move the motor in either direction if needed..just not sure if i need to...when trimed out for best speed and RPM the prop will vent if i make hard turns..but is okay in lesser degree turns...if I trim out more the boat starts to porpoise but speed does increase 3-5 depending on load..<br />one thing i have noticed is that if i let go of the wheel it goes hard to the right within 3-4 secs and will do full right hand circles if i let it...kind of scary the first time it did it to me..not sure how to correct this..<br />If i trim it down more speed falls off some -3 but the RPMs only fall about 200...I would like to go to a SS prop and think the extra 1/2 inch diameter SST should be okay but just wanted a better opinion..<br /><br />and if i need to move the motor around or mess with it any i'm up for it..<br /><br />so what do you think...

 

[Dhadley]

Re: Yet Another Prop Question....

If youre willing to play with the set up, I'd suggest going with the 17 ss. However we really should verify the speed and tach before spending money. <br /><br />I'm not quite sure what to think about your plugs in the other post. I really havent had time to sit down and think about it much. Work keeps getting in the way.

 

[kirkland]

Re: Yet Another Prop Question....

I understand....here too....going out at lunch to try a test run with GPS so i have better data...will post in about three hours the results..<br /><br />i have some food for thought on the plug thing but i will post it over there to keep things going in the right direction here...<br /><br />Again Thanks Dhadley an all who are helping.<br /><br />Jeff

 

[kirkland]

Re: Yet Another Prop Question....

I'm looking at the prop that is on there right now and the blades are real thin like 1.236 mm thick at the tip and 1.874 mm thick at the base does this seem thin for an aluminum prop of this size...?? i'm about to head for the lake for quick test run with GPS...

 

[kirkland]

Re: Yet Another Prop Question....

okay here are the figures with just me and half fuel 5900 rpm planed in about 5 seconds 41.5 on fishfinder 35.6 on GPS 13 1/4 X 17 aluminum... do these figures come out better than before???

 

[moderator1]

Re: Yet Another Prop Question....

Nearly 25% slip...something is still not right...Dhadley will be back in the am I would guess.

 

[kirkland]

Re: Yet Another Prop Question....

how are you calculating this...what i my gear ratio?

 

[Dhadley]

Re: Yet Another Prop Question....

I'm getting right at 10% using 35.6 mph. Not bad.<br /><br />Now we have a tough decision to make. Youre doing good with a 17. But with changing the set up we might could use a 19. Hummmm....<br /><br />Whats your normal load?

 

[kirkland]

Re: Yet Another Prop Question....

normal load is three to four adults with 250lbs gear, 13 gals fuel, three batteries, 30 gals water if livewells are full...

 

[Dhadley]

Re: Yet Another Prop Question....

OK. I'd suggest a 17. Fine tune the set up and if you get to a point where you need more bite, it can be added easily. I'd rather see you do that than buy the 19 and have to reduce efficiency to gain rpm.<br /><br />With your light load the 19 might work fair but with a normal load we want the motor to live.

 

[Dhadley]

Re: Yet Another Prop Question....

PS -- I gotta assume ya gotta hate what NASCAR did to DEI.

 

[kirkland]

Re: Yet Another Prop Question....

I agree... i'm looking at a 13 1/4 X 17 stihletto..any views on this prop...it's a ebay item....<br /><br />What did i miss..what did NASCAR do ...other than all the b.s. about gears and tranny....i wish they would let these guys race...i understand the saftey stuff but let em be...anyway i don't want to get started on that i could be here for days and my soapbox just isn't that comfortable....

 

[Dhadley]

Re: Yet Another Prop Question....

Good choice as long as its not been reworked. How much are they wanting?<br /><br />Thats the point -- the gears. They found out the DEI cars were using real low ratios and took them away. Theres a couple of ways to build those motors. One is to build lots of torque. The other is to build a motor capable of higher rpms and use that to get into and off of a corner. Thats why they werent great on restarts but real bears in the corners. Now they have to revamp their whole engine program. Itll take time.

 

[kirkland]

Re: Yet Another Prop Question....

I don't know the history on this prop but right now its around $135 not willing to go much above 175 unless it was a new one...<br /><br /><br />I feel like they are taking the fun out of the sport i remeber when you could buy a car that looked like what they we racing in...acutally it was the same car with heavy modification...I think that's what the STOCK referred to anyway i wish they would just let'em race....<br /><br />Thanks for all you help by the way...on the other thread i'm getting some clear fuel line and trying to borrrow a portable from someone local to test with...6:1 ratio is a little much i think....

 

[Dhadley]

Re: Yet Another Prop Question....

I took a quick look at E-Bay. I found 2 17" Stiletto props. Neither one will fit your 70. I hope youre looking (bidding) on a different one.

 

[kirkland]

Re: Yet Another Prop Question....

the part number he gave me was 21317 which led me to the stiletto... he only describes it on the site as a OMC 13 3/8 X 17 SS

 

[Dhadley]

Re: Yet Another Prop Question....

Yep, thats the right part number for a 17 that fits your motor.