prop/performance question

[spete]

I have an 18 ft tunnel hull Gulf Coast bay fishing boat with a 115 hp motor. The hull is similar to a Boston Whaler/swept v-bow that flattens out towards the middle/aft of the hull. I currently have a 4-blade SS prop that's marked 16X13 TC. Boat has plenty of hole shot and not a great top end. will probably do 35-36 mph top end at WOT turning 5500. Cruising at 30-31 mph takes about 4900-5000 rpm's. I'm wondering if there would be any benefit to going to a 3-blade prop and different pitch to get more top end and cruise more efficiently? Is the 16X13 ... 16 pitch and 13 inches? One revolution means a travel of 16" ... guessing ... can someone explain? I've tried the jack plate in many different positons/trim configurations and the numbers stated are about th max i can get. Also, wondering how the 4-blade pitch numbers correlate to a 3-blade. Any suggestions on how to improve my cruising/top end performance and good/bad brands of props would be greatly apprecieted!

 

[zzzzz]

Re: prop/performance question

spete-5500 rpms is the magic number...one of the inherent features of a 4 blade is to lose top end speed...if you go to a 3 blade try a 15 pitch and aim for 5500 rpms at wide open throttle...when diameter and pitch are mentioned,the diameter is the first number and pitch is the second...and you are correct about one revolution means you travel that far forward(15 pitch=15" forward)except we're dealing with water so you get about 80 percent of that due to slippage...as for a good brand,try Solas-nice thick blades,good quality

 

[spete]

Re: prop/performance question

Thanks Z ... the prop is stamped 16X13 on the inner brass/bronze hub part that the prop nut tightens on to. The only marking on the outside of the prop says ... 16. Does this mean i have a 13" prop and 16pitch .... I wonder if a prop shop stamped this incorrectly? 13" diameter/16 pitch seems more likely. Didn't know if a 4-blade would measure diameter differently? Also, if I like to run shallow and raise the jackplate, is the 4-blade going to hold better/cavitate less? Guessing that there's a trade off of shallow running ability and top end speed with a 4-blade. Would really like to go faster, wonder what I would lose with a 3-blade really? I have heard that 4-blades create less vibration and help improve lower unit life... any truth to that? Is there any way to tell what the cup/rake is on my current prop and does that make any significant difference? A local dealer carries the Solas props and they do look pretty nice, not real sure what to look for in a good quality prop - except that it's probably going to be over $300

 

[zzzzz]

Re: prop/performance question

spete-measure your 4 blade straight across tip to tip and thats diameter...you're right,13 diam sounds more like it...a 3 blade is measured from center of prop to tip of a blade-then double it...a 4 blade will always have 3 blades in the water so they will hold better shallow running and in tight turns but they always lose top end..I don't think there's any truth to longer lasting lowers from 4 blade usage-thats pushing more water/more strain on gears etc..we sell Solas-13 X 15 = $275(free UPS to Spicewood)

 

[Hopsdak]

Re: prop/performance question

Spete, I have the exact same set up as you!<br />Only difference is i have a 130. If you find a good prop lemme know. I now have a 4 blade and it cavited badly. I had a nedski installed and it fixed that but, it dropped my top end by 3-5 mph.<br />I'll look this weekend and see what it has stamped on it.. i was thinking of going with a 3 blabe double cupped with a 16-17 pitch. here are some pics..<br /> Portside <br /> Nedski side <br /> Nedski aft <br />Later, Hop<br /> hopsdak@hotmail.com

 

[spete]

Re: prop/performance question

thanks Z ... will keep the Solas in mind when I finally figure out what I should try. Would like to find someone locally who might let me test some different sizes out. I measured the prop and it actually only measured 12 1/2 inches from tip to tip. Wonder if this prop has been re-cupped or re-worked. I bought the boat a couple years old so I don't know the history of the prop? Wonder if 1/2 inch -1/4" on either side would make that much of a difference in speed or performance? I have a compression plate (aluminum) similar to the Nedeski but shorter - sounds like that could be hurting my top end as Hop indicated. <br /><br />Hop ... what is your top end anyway? I have a '99 and it looks like they've changed up the leaning post a bit - mine is screwed on to the deck. Is that a live well on the back? Did you put the storage hatch on the front of the leaning post or is that how it comes now? Mine has a livewell (Square) in the floor. Not sure if square is the best choice for a livewell but I've never had trouble keeping shrimp alive in there. Plus, I throw mostly artificials now anyway so it doesn't make much difference. My Access hatch is in the rear of the l/p and i have a cooler in the back that blocks it. Want to add an access hatch in the front like yours is set up. Wanted to ask you... does your center console have some give to it? and did you add the foam grip on top - nice touch. Love the boat all and all - wouldn't want anything else - except maybe a 25' Vari-side!!!

 

[zzzzz]

Re: prop/performance question

spete-losing 1/4" per blade wouldn't cause a drastic performance drop but a minor one

 

[Hopsdak]

Re: prop/performance question

Topend is around 32mph on my gps @ 5200. I wish i would have checked it before i put the nedski on there. I had it up to almost 5600-5800 before the nedski.<br />I picked my boat up second hand about 3 weeks ago. It's a '00 model and they changed the leaning post up on it that year. The live well is in that. All i've done to the boat is add a dual battery set up and a lowrance lms-320 gps/fishfinder. The padding on the handrail is pipe insulation you can find it at a hardware store. It works great for sticking jigs on to keep them off the console.And what do you mean about the center console giving? i've noticed that it has some sort of rubber gasket around the bottom. Those verisides are sweet! They even have a crapper under the console!! That you can stand up in!Console pic...

 

[spete]

Re: prop/performance question

Good to know Z ... is there a standard prop cupping to look for? Are they standardized from maker to maker? I've heard of terms like double cupped ... rake degree ... pregressive pitch ....etc. Do you just go with a reputable maker that's optimized the hydrodynamics and go with them and adjust the pitch accordingly till you get a good fit? Will a thicker, heavier brand of prop like Solas turn fewer RPM's? Just looking for a few pointers before i dive into my prop purchase. Thanks for all your feedback!

 

[spete]

Re: prop/performance question

Hop - I guess if I'm getting 35 mph @ 5500 I should be happy. Just seems like that boat should go at least 40 and cruise comfortably at 34-35mph. Will let you know if i find a better prop for the set-up.<br /><br />My center console has some give to it if you tug on it forward or backward. the guy I bought it from said that it was always like that and that he just figured that it was designed to give a little if you run aground - maybe an 1" of play/rocking from fore to aft.

 

[spete]

Re: prop/performance question

ZZZZZ . ... you suggested a 13X15 - -wouldn't I want a 13X17 if i were giong after a better top end than the 13X16 I'm currently running - or is the 3-blade a little different?

 

[Hopsdak]

Re: prop/performance question

If you have any questions about it contact Susan Gilley @ GCBOATS@sbcglobal.net or 713-477-7119. It sounds like it's lose to me.. I havent had mine move that much. I know it gives some but, i think that's to help dampen the hull movement from the console.. i'm not sure but, i'd definatly give her a call and find out. Better safe than sorry.. It would suck to have the console come loose on ya.<br />LMK on the prop..<br />--Hop

 

[sharkcat]

Re: prop/performance question

For props try this guy he did the business for me Email: Propdok@aol.com or his website www.BoatpropsRus his name is Phil & he has probably forgotten more about props than most guys know Give him a try.I put hustlers on my boat on his recommendation & Im very happy!!!

 

[zzzzz]

Re: prop/performance question

spete-if you need to gain rpms you need to de-pitch....one inch of pitch=prox 200 rpms

 

[spete]

Re: prop/performance question

Thanks for the info - may go up one in the pitch and see what happens to my top end - appreciate your feedback!

 

[Hopsdak]

Re: prop/performance question

I checked my prop out this weekend. It has a 16 stamped on it. And it's four blade.. So i'm asuming that it's 16 pitch and i didn't have a ruler to measure the dia. I also installed a nice fuel/water seperator. It was giving me fits on sat so i pulled the plugs that i put in last week and decided to check the gap. I thought they were pre gapped out of the box... i guess not. I checked it and it was .019 so i opened them up to .035, Is that gap too large? This is on a Johnson 130.<br />--Hop<br />P.S. I also check my console. There is little to no movement on it..

 

[spete]

Re: prop/performance question

Hey Hop - thanks for the e-mail to S.Gilley - she gave me instructions on how to tighten the console - really nice gal - even gave me her ph# and said to call with any further questions. About the plugs, not sure what the gap should be ... .035 sounds closer to the right thing but that would just be a guess. Ask the dealer or look in your motor manual or check inside/outside the cowling for a factory sticker and that will give you the gap. Good luck! I've been wanting to put a Racor filter on my boat just haven't gotten around to it. That's next on my list. There's a GC owner's tournament in October down on matagorda bay ... too bad that's my annual dove hunt!

 

[Hopsdak]

Re: prop/performance question

LOL I'm going dove hunting to! My uncle owns a ranch in Mc Allen and we hunt it every year. Nice and fat white wings down there. Well i regapped the plugs and the motor ran great!! I couldn't open it up for very long. It was really rough this weekend. I did manage to find one flat spot in the bay and hammered down, the motor rapped out at 5600 rpm for about 15-20 seconds (too rough to stay wot that long).. So i'm thinking that this prop might be alright. I couldn't tell ya what top end i got cuz i couldn't watch the gps and the swells at the same time.. heh

 

[spete]

Re: prop/performance question

We hunt down close to hebronville ... white wings used to be non-existent and now they're getting to be a pretty common sight. Glad you got the gap down - had to freak you out to think that the new motor was going south on you. Good luck and tight lines!<br /><br />p.s. - I have a buddy staying bayside at a Jamaica Beach canal house rental - any West Bays spots I could tell him to hit?

 

[Hopsdak]

Re: prop/performance question

Tell him to check out www.texascoastalangler.com <br />Go to the angler reports and check it out!<br />I havent fished west bay.. Other than San louis pass. The fish are hitting pretty good on croakers. In east bay, dollar reef and hannas are going off right now.