Prop advise 16.5 foot bowrider 3.0 L Mercruiser

[Big-E]

Guys after i spun my prop in the late summer i went hunting for a new one. Prop shop suggested a 15x19 since the old 15 x 23 would only let the motor spin up to about 4100 rpms. I got a brand new 15 x 19 Mercruiser prop (sealed in box) for $50 bucks new so i jumped on it. When the rpms started to get near 5000 i let up. I do not know how high it will go but i stopped at 4900 rpms and she wanted to go way more. Should i be running a 14.25 x 21 on this boat? I checked online with other boats like bayliners in the 17 foot range and the 14.25 x 21 is the prop they use. My current prop will make a great tubing/back up prop. <br /><br />The boat screams up to about 35 mph though... <br /><br />I know the 21 pitch prop will lower max rpms by around 400 right? <br />Thanks,<br /><br />Big-E

 

[Eugene Winkle]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

Check with the manufacturer to see wht the specs are on recomended RPM. My Johnson 150 is somewhere around 5200-5700 top speed.

 

[Eugene Winkle]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

Sorry!! I didn't pick up on your question being about an inboard ooutboard until after I posted. Wish I could help out.

 

[walleyehed]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

The RPM difference depends on prop style and where you are in the powerband now.<br />Something that would help more than anything, is telling us what the Max recommended RPM for that engine is.<br />If the prop shop told you to go to a 19", I would guess they figure the RPM will be in the 5200 range....but what is Max recommended??

 

[moderator1]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

Make and model of prop would help too.

 

[Tail_Gunner]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

HP/Model WOT RPM Gear Ratio <br />3.0 L 135 4400-4800 2.00 A1 <br /> <br /> <br />Currently i am using a 18x14.5 on a 17 ft open bow,the boat runs @ 5000 @ 42mph. However i am bow heavy and and it takes very little to get this damm thing porpising, so for my self i may go to a 19 or 20 four blade and vent it a bit which i hope will give me a better hole shot and keep the bow up in rough water.

 

[Big-E]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

Sorry should have been a little more specific. RPM range for the 3.0 is like Tail-Gunner posted 4400-4800 rpms. Id like to have her propped up near the upper end of the rpm range. I dont remember the name of the 15x19 mercruiser prop i got but the box stated its a factory equipped prop. Prolly just the standerd one they outfit on all there outdrives. <br /><br />My boat weight's around 2200 lbs wet. The boat is pretty light and that 15x19 prop gets her on plan very quick. But she will overrev if im not careful. THe old worn out 15 x 23 would let her cruise at 35 mph at about 3200 rpms. Only problem was it wouldnt go over 4100. Id like to have the cruise speed back into the 30's and have her wind out right up to 4800. <br /><br />My best guess is the 14.25 x 21 should get me down in the rpms range i want to be. Or should i get a new 14.25 x 23.. I tried asking some shops if i can borrow a prop but they are scared since we have very skinny water here. <br /><br />Also let me add i have no foil or tabs, hull is fiberglass v hull. My current prop will make a great watersports prop, my goal is to just have the proper prop on her that will let me cruise around 30 at 3000 rpms, and max rpms up near 4800. <br /><br />thanks, <br /><br />Big-E

 

[walleyehed]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

Tail_gunner,<br />

Currently i am using a 18x14.5 on a 17 ft open bow,the boat runs @ 5000 @ 42mph.

This would be a slip ratio of less than 2%...Impossible. If you're running GPS speed, your tach is off.<br />With a modest slip of 12%, 38-39 would be top speed achievable with that prop at 5000RPM..<br /><br />Big-E, the prop you have is likely a Black-Max...I think I would consider a Good SS prop in the same pitch, or maybe go to a 20". You want to stay close to 4800-5000 if ya can...that'll give best cruise and longest life of your engine.

 

[Tail_Gunner]

Re: Prop advise 16.5 foot bowrider 3.0 L Mercruiser

posted February 07, 2006 08:55 PM <br />--------------------------------------------------------------------------------<br />Tail_gunner,<br /><br />quote:<br />--------------------------------------------------------------------------------<br /> Currently i am using a 18x14.5 on a 17 ft open bow,the boat runs @ 5000 @ 42mph. <br />--------------------------------------------------------------------------------<br /><br />This would be a slip ratio of less than 2%...Impossible. If you're running GPS speed, your tach is off.<br />With a modest slip of 12%, 38-39 would be top speed achievable with that prop at 5000RPM..<br /><br /> I'am sure you are right,the tach and the speedo jump a bit. Actually i believe its 5100 @40-41 non gps reads just gauges. However Walleyehed i am runnnig a 17.1 Starcraft open bow Euroliner with a 3.0 mercrusier,and i really am or the boat is having tough time staying on top of wave chop say eight inches to a foot. going up out of the hole to full plane is quite smooth but soon after the bow will start dipping (porpisng?) and proceed to knock my teeth out. Will going to a 4 blade prop create enough lift to eliminate the bow from dipping and starting some hard plowing or am i just over thinking this and its just due to the overall lenght of the boat running in a chop @ those speeds?