Prop blowout cavitation/ventillation w/115 merc

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Mark,<br />What you said re "shifting weight to front" is what im thinking too. <br /><br />Fist thing done (before I ever took boat out)was add a 18gal tank and trolling battery across front-eliminating the 10gal one in rear.<br /><br /> That really changed the performance. <br /><br />(edited-Found bow to bounce less and figure the ventillation issue probibly got worse at this point-taking weight from back and putting it up front. Thats ok cause gotta make it work with it up front)<br /><br /><br />Looking at my gear now and planning to add all weight i can to bow end-anchors.<br />There really isnt any more "heavy stuff" that would go up there though- my wife never fishes with me (ehh gahd, did i really say that!) <br /><br />Thinking the turbo 4-blade for speed/lower blowout(4th blade=more surface area of prop) and still give me mid 5s rpm(?). If not then have reproped down slightly. <br />Bought it online for 200. preferred a 22p but....price was right.

 

[ob15]

Re: Prop blowout cavitation/ventillation w/115 merc

I'm just curious, what should your WOT rpm's be? It hasn't been mentioned yet and I wonder what Dhadley & Kenny think. That 23P 4-blade may be too much especially if it's cupped unless it allows for some additional trim and you can get the rpm's back up. You're definately getting there. It's amazing what cupping does for ventilation. I've been there & these guys really help.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Having just bought this boat with the older 78 merc 115 it ran ok, but still did alot to motor as i needed to feel confidence in it. You know, rebuild fuel supply,rebuilt pump,rebuilt LU,decarbed,carb job,distrib. cleaned, etc...I-boat forum was sooo helpful.<br /> Was fun (this time!)Runs great now. Gotta do clams link/sync.<br />Love the look and sound of these inlines!<br /><br />Im still keeping an eye out for late 80s-early 90s yamaha/merc/suzuki 90,115,140hp-Not sure why-trying to get as new as possible.<br /><br />Thinking newer/(maybe smaller) for fuel efficiancy.<br /><br />(edited later)After much research on this site-maybe a pre 90's omc V. Ive allways been a merc guy, but nothings carved in stone.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

5000-5500

 

[ob15]

Re: Prop blowout cavitation/ventillation w/115 merc

I'm sure the experts will reccomend 5500 min. I'm not a Merc guy so can't say what to shoot for. Good luck & keep the updates coming. It will be interesting to see what the 4-blade does for you.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Having been around this board (and others) I do know not to "lug" motor, so figure that prop needs tuned to give around 5200-5500 empty. <br /><br />Dont plan to add much rig weight other than filling livewell(15gal) and the occasional 60lb flathead(s). Usually fish alone.<br /><br /> Also figure 21P SS spare will run higher rpm for those times when more people are with me.<br /><br />Just for kicks, when I get that 4-blade turbo and the spare 21P SS (thats having cup added now)this week to lake for test, though id try a stingray dolfin as I have one just sitting around and AV plates allready drilled for it (came w/LU bought as spare).<br /><br />Anxious to report results.<br />Then hopefully can go about the business of using the boat! Never been productive for spring flatheads/blues to date, but each year I learn.

 

[ob15]

Re: Prop blowout cavitation/ventillation w/115 merc

You might want to hold off on the fin until you test the 4-blade. That way you will have a good comparison.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

wondering what prop blade would be a low rake design in 3 or 4 blade?<br /><br />Yeah I agree re the fin. It wont do any good I figure, just gotta try for he!! of it. I got this 2-blade merc prop and gotta try it too-I know it'll prob be worthless, but gonna try it anyway. Nows the time.

 

[walleyehed]

Re: Prop blowout cavitation/ventillation w/115 merc

I think you want to stick with moderate rake props...low/no rake is usually for heavy, slow boats.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

So what is a "moderate rake" prop? Can you give me Brand/model please.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Rake i know is measured in degree, but dont see it talked/used much in a measured sense. More like "that one got a high rake" or... ya know.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Im just trying to get it straight what type or style prop to try that might not otherwise get tested. Not trying to beat dead drum. Nows when its got to happen cause once I start concentrating on those fish I wont care about boats performance beyond getting me there.<br /><br />So the idea being not to go too far +/- from round ear type. OK<br /><br />I can understand prop mfg's desire to not over complicate an allready confusing science of matching props many design chariteristics to the limitless possibillities of setups (hull x, weight x,water type x,usage x....)by listing degrees of rake and percent of cups too. Prob most buyers wouldnt care anyway-just go by experienced recomendations.<br /><br />Probibly most important to accuratly test the props performance on my rig anyway so future tweaks can be made.<br /><br />Think a good topic would be "how to analize your setup". Looking back at my posts I see alot of improvment to my approach.<br />And its still fresh in mind this week.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Have several more that plan to test:<br /><br />1-SS (brand? heavy used prop)21p Having cup added<br />Turbo 4 blade 23p<br />Laser II 23P<br />Yamaha 23P<br />Laser II 24p

 

[Dhadley]

Re: Prop blowout cavitation/ventillation w/115 merc

On the ss prop youre adding cup to -- are you increasing the amount of cup or the length of cup?

 

[ob15]

Re: Prop blowout cavitation/ventillation w/115 merc

Dh, I believe that prop didn't have any cup. Hard to believe that a SS prop doesn't have cup though.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

That prop was what came with the boat and though it looked ok, it wasnt obvious what brand/type it was-looked... "custom" or modified. <br /><br />Prop guy and I looked at it on the pitch block and the parabolic curve was missing about 1/2 inch like it had been ground down from repairs (?). Maybe last guy was modifying it for the hull though...hmmm been wondering that.<br />(added later)Maye orig owner ground that prop so it cleared the TT? Who knows. Maybe blade took a big hit too?<br /><br />Prop guy said there was no cup (I think). I'll have to ask him again. Anyway, Didnt figure prop was very sale-able, so told him to add pitch and cup or double cup at his descretion. If it no work its no loss-use it as spare.<br /><br />10 days ago didnt know "cup" or "rake" on a prop-all I knew was pitch and diam., today I could identify it and would know to look at leading,trailing etc and rake as straight....

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Originally posted by Dhadley:<br /> On the ss prop youre adding cup to -- are you increasing the amount of cup or the length of cup?

He's (prop guy) in control of that. Week ago I didnt know enough to direct him. Thats changing a little as I educate myself.<br />Whats your thoughts? <br />As it is the props been "ground" taking blade area away from the trailing edge wher cup would be.<br /><br />Addding all cup possible ( he can add)is what he and I figured.<br /><br />Add to that- I dont know how good he (prop guy) is at this point either. Do know he has been very helpful.<br />I dont know what a "high end" prop shop has for eqpt. -would like to know.<br /><br />Figure he is a heat n beat shop.

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Doing some deep research on I boat (what a wealth of info!) ran across JB's post re "basics of prop selection" (great writeup!)<br /><br />"Smaller diameter props in a given pitch tend to be "slightly" faster for the same reason..LESS drag from less blade area. The smaller diameter props are usually better suited to "Lighter" boats.<br /><br />An exception to this is in High-performance applications where the prop blades break the water's surface and a larger diameter prop is preferred for better performance."<br /><br />Maybe testing a smaller diam prop? Modifying prop diam?

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Finally got some nice weather today. <br /><br />Tested a laserII 24p and WOT @5300 (thats empty).Hole shot course went down.<br /><br />The ventillation wasnt too bad-could (almost)live with it (if i didnt know better),but have to remember to keep trimming in.<br />Can trim out about 15degree, then starts slipping.<br /><br />Screwed up and 4-balade turb 23 and yamaha 23P SS both 41/2 hub so have to buy a bigger motor to use them. <br /><br />Still have to test :<br />1-SS (brand? heavy used prop)21p Having cup added<br />23p laser II

 

[jameservin]

Re: Prop blowout cavitation/ventillation w/115 merc

Decided to repower this rig with a new (non-current 2003) 90 hp 4-stroke mercury EFI motor. The gear ratio change will require smaller pitch (so I am told).<br />Plan to get to it in next few days, providing the snow doesnt come!