Prop help

[snal]

I have a 1996 Rude 90hp on a 1996 Smokercraft 17.5' deep-vee aluminum boat. I have a 13x13 that came on the motor, and a cupped version of the same as a spare. I get light load top speeds of 40-42mph, and somewhat heavy load speeds of 35mph...which is about all I'd expect...but my WOT rpm is 5100 max. My research has shown that props most recommended are around 13.75 x 15...and I was given one of these...haven't tried it yet...but wouldn't that slow my rpms even more?<br />Any advice?<br />TIA

 

[Dhadley]

Re: Prop help

Something doesnt sound right. You are correct the larger prop will pull the r's down even more.<br /><br />Which 90 do you have? A crossflow or a looper?<br /><br />BTW -- welcome!!

 

[reeldutch]

Re: Prop help

i would defently check the motor out because a 13X13 on a 90hp with a 17.5' aluminum boat only spinning 5100 sound really not right.<br /><br />check your compression something doesnt sound good.<br /><br />good luck

 

[reeldutch]

Re: Prop help

sorry dhadley you out typed me.

 

[Dhadley]

Re: Prop help

I must be getting better at this hunt & peck thing.........

 

[snal]

Re: Prop help

I'm not sure...it's actually an 88 special (90 non oil injected) and a carb model.<br />I haven't used the boat much in the last few years...but now we have a camper at the lake, and use it every weekend. Most of the previous use was with 2 adults and fishing gear. I wonder if the tach could be off?...the speeds seem to be fine. Holeshot is fine with light loads, a bit slow with 5 adults aboard. Trim range is very low, I could'nt trim at all without prop wash or bouncing, until I lowered the engine about 2" from the dealer mounting. I could lower it another inch.

 

[snal]

Re: Prop help

That looks just like my engine...I just had mine serviced....new impeller, plugs ect. The compression was checked, and was well within range on all cylinders (135#...?) average. This engine has very few hours for a 1996 model.<br />Thanks for the welcome...and help!

 

[Dhadley]

Re: Prop help

Thats a crossflow. <br /><br />OK, at 5100 rpm with a 13" prop your theoritical speed is 32 mph. So either the tach is off or the recorded speed is off. <br /><br />If you had to lower the motor, somethings wrong with the prop most likely. Lowering the motor is absolutely a last ditch effort in set up.<br /><br />What was the rpm when the motor was mounted higher?

 

[snal]

Re: Prop help

I can't remember what the rpms were before lowering the motor...that was when it was new, and I'm 45, and suffer from CRS <G> I lowered it to give some trim range, which was nill at the higher setting...the anti-cavitation plate is still about 1.5" above the keel.<br />I'm going to the lake this evening, hopefully to try the other prop, just for the heck of it. I'll double check the current prop size. If I remember correctly, my spare is the same size...but cupped...the current one has no stamping on it, so I'll check the size when I remove it.<br />Thanks for the help guys!

 

[reeldutch]

Re: Prop help

a crosflow v4 on a 17.5' boat with a 13"prop sounds very odd to me. you must have a heavy boat.<br /><br /><br />i had a v4 on a 17' fiberglass boat with a 13 1/4 X 17 ,5600 with fully loaded boat 3 people and some chop in the bay.<br /><br />something is wrong check your compression.<br />or you have a 13 X 17.<br />thats my guess.

 

[snal]

Re: Prop help

Dry weight is 1260#...maybe I'm way off on the current prop size...if so...then the 15 pitch may help.<br />Thanks!

 

[snal]

Re: Prop help

Here's the boat...hull is unchanged from my 1996 model.<br /><br /> http://www.smokercraft.com/famfish/millentia.htm

 

[reeldutch]

Re: Prop help

yep but you are only having 5100 rpms<br /><br />check the prpsize and also compression.<br /><br />something is funky here.<br /><br />if you have a 15 pitch and only 5100 rpms something is wrong .<br />if you have a 13 pitch and only 5100 something is terrebly wrong.<br /><br />you should be able to spin a 17 pitch prop and getting at least 5500 rpms<br /><br />let us know

 

[snal]

Re: Prop help

I found my service receipt...compression is..<br />#1 125 #2 125 #3 130 #4 125.

 

[reeldutch]

Re: Prop help

thats good news<br /><br />no problems there.<br /><br />now we need to know the prop size be accurate.<br />also<br />check for spark you might have lost a cylinder.<br />wich is not uncommon.

 

[snal]

Re: Prop help

Update...I checked the current prop last night, there are no markings telling what size it is, just a michigan prop number (012051)...it appears to be a 13 x 19...rather than a 13 x 13.<br />So...it looks like my 13.75 x 15 should get the rpms up in range, the only info I can find is on the newer V4's 4500-5500, does that sound about right? The 15 pitch should get me around 5500 I'd think...not sure what kinda holeshot I'll have.

 

[Ron G]

Re: Prop help

ill leave it to the pros but looks like the 15 should get you a better hole shot than the 19

 

[Dhadley]

Re: Prop help

The smaller prop(s) will get the rpm up but your overall efficiency and speed will go down. Basically youre looking for about 700 rpm. To get there from a 19" prop, without changing the set up, youll have to go to the 15 most likely.<br /><br />Now the numbers start to fall in place. With the 19 at 5100 and 40-42 mph youre at about 10-14% slip. Not too bad but could be better. Thats most likely the product of prop design and / or condition.<br /><br />We'd rather see you work with a better design 19 and change the set up. That way you should gain speed which means youll gain overall efficiency. <br /><br />If youre set on not using a 19 we'd rather see you go with the 17 and then use the set up to gain more rpm.

 

[snal]

Re: Prop help

Thanks! I'll try the 15...since it was free, and I can probably borrow a 17 (lotsa helpfull folks at this campground)...once I find what works best, I suppose I should look for a quality prop, perhaps in stainless?<br />I've also been reading about the smart tabs in this forum...not to crazy about drilling my transom...but it sounds like they may be the answer to my lack of trim range. Wonder if using the tabs would effect prop choice.

 

[snal]

Re: Prop help

My spare prop turns out to be a 13 x 19 as well, but it's cupped, and the blades are much thicker than the Michigan prop. I remember that there wasn't much difference between the two for performance.