Some prop guidence please....

[jheron]

Well the rebuilt 76 115 tower is now broke in and ready to take up to WOT <br />I tried a 19" X 13" first and I could only get up to about 4500 rpm I then tried a 17" prop and 35 mph at 4900 was all it will do. The prop dealer says that something must be wrong?<br />The boat is a Lowe 170 deep v Fish n ski I think the boat alone weighs around 1100 lbs plus the tower and a 9.9 kicker with better half and myself, cooler, skis... so maybe around 1700 lbs gross rough guess.<br /><br />What do you guys think? is my tach off maybe? or is the dealer just on crack and I need to drop another pitch?<br />Any and all advice is appreciated <br />Sincerely Jon

 

[sangerwaker]

Re: Some prop guidence please....

Definitely something wrong in the tach system. Going to a 17 from a 13 should LOWER the RPMs.

 

[wilde1j]

Re: Some prop guidence please....

He's got dia and pitch reversed. 13" dia X 19" pitch and went to a 13x17. What had it done before the rebuild?

 

[Clams Canino]

Re: Some prop guidence please....

It sounds like the tach might be off, I wish I could hear it. Is the boat alum or glass?<br /><br />I'm getting 1100, 400 for tower and gas, 200 per person, 100 for kicker.<br /><br />I know I use a 17 on my boat for day to day use and a 15 for pulling multiples.<br /><br />How is the hole shot with the 17p? Is it stainless or alum? Is your WOT rpm after trimming up a bit underway?<br /><br />-W

 

[jheron]

Re: Some prop guidence please....

hehe ya I have it reversed!<br />I dont know what it did before I rebuilt it, the boat it was on went to the dump and there are no numbers left on the old prop <br /><br />I wish you could here it too clams I wont be back on the water again till next weekend and I will get a sound clip of her for ya if I dont have it figured out by then.<br />The boat is alum and I think the tach is working fine at least at idle it is. I have a manuel shaft driven tach and 1000 rpm on it is pretty close to 1000 rpm on the new faria tach on the boat. The motor sounds awsome!! and like it has alot more scream left in her while topping out at the 4900 rpm?<br />I still dont have the trim working yet but should have it fixed by this weekend. <br />The props are 3 blade alum michigan wheel vortex and the hole shot seems ok but I have nothing to judge it by because my other boat is a 10' Zodiac It has alot of torque... it will jump from 4000 to 4900 in the blink of an eye but with 4 people on the boat I know it wont pull me up on one ski without me drinking in half the lake <br />I am going to double check the timing, tach at low rpms and that the carbs are opening up fully other than that I dont what to do?<br />Does the fact that shes doing 35mph at 4900 rpm indicate a faulty tach as well?<br />Well thats enough rambling for me <br />Thanks for all your help.<br />Jon

 

[jheron]

Re: Some prop guidence please....

Well the tach still checks out with the manual one up to 1000rpm any ways, I cant check it at a higher rpm until I get it out to the lake but the needle does seem to climb like it should when accelerating? I double checked the pointer, max advance and pickup and all bang on... carbs are opening up like they should I even checked compression and all is as it should be <br />Any other suggestions guys?<br />Maybe I just need to drop to a 13X15?? What do you guys think? <br />thanks again!!<br />Jon

 

[jrampey]

Re: Some prop guidence please....

If I calculate the prop efficiency I get about 11% slip for a 2:1 gear ratio @4900 RPM and 35 mph... 17% if the gear ratio is 1.87:1. 11% could be close to real.

 

[jheron]

Re: Some prop guidence please....

Ok so I guess thats good news! Acording to my seloc I have a 2:1 ratio. So is a 11% slip acceptable?<br />Thanks <br />Jon

 

[jheron]

Re: Some prop guidence please....

Well after some reading 11% seems fine. So does droping to a 13X15 for daily use and a 13X13 for big loads and doubles seem reasonable, or am I a little under powered? The boat is max rated for a 115hp but that would be at the prop and mine is rated at the crank.<br />Jon

 

[walleyehed]

Re: Some prop guidence please....

There would be very little noticable difference in prop or crank rated engines of this size, given they are both healthy.<br />It sounds as though you are lacking some power though...I just got finished working on the same engine on an 18-1/2ft deep-v fiberglass rig that will turn 6100RPM with 3 on board and full fuel, with a 13X15....a bit over 2000lbs.

 

[jheron]

Re: Some prop guidence please....

hmmm... interesting, I wonder if its a combination of all the jugs being .015" over and using all low dome pistons have degraded the hp? I wouldn't think that would make that much of a differance though?<br />Well hopfuly the dealer can get a 15 in for tommorow and I can give it a whirl this weekend <br />I wonder if engine height is causing me grief I just set her on the transome and bolted her down without knowing how important height is <br />The anti cavitation plate is about 3/8" above the keel... hows that sound? <br />Thanks Jon

 

[jheron]

Re: Some prop guidence please....

Now I am wondering if I have a water ingestion problem The bottom 2 plugs look way to sparkly clean! I have a feeling that I might have a slight leak in the exhaust plate <br />Oh well you cant win them all! I ordered a new plate and merc gaskets so I will try again....<br />Jon<br />PS any advice on motor height?

 

[walleyehed]

Re: Some prop guidence please....

If you are running low-dome pistons, have you set the timing accordingly????

 

[jheron]

Re: Some prop guidence please....

Yep I used a dial guage to set the pointer and followed Clams link and sinc post...<br />Jon

 

[jheron]

Re: Some prop guidence please....

If she is ingesting water will it be very obvious? The 2 bottom plugs don't really show water on them but I figure it would evaporate pretty quick? They are very sparkly clean though (unlike the rest which are a lovely oily black) which makes me worry This would also explain the apparent lack in hp ... rite?<br />It doesn't sound like it's missing ... its real smoooth....<br />Jon

 

[walleyehed]

Re: Some prop guidence please....

Look at the piston tops in the bottom 2....are the tops shiny clean?<br />We also have one definite thing in common on the bottom 2 cylinders....the bottom carb...

 

[jheron]

Re: Some prop guidence please....

Update! <br />Well she was ingesting water through the exhaust plate, but not enough to effect the wot rpm, my troubles where all related to my trim not working <br />I have never had a boat with trim before so I had no idea what a differance it would make!<br />Now with the 15 pitch with the motor trimmed up she will now do 37 mph at about 5700 rpm Thats with a moderate load, probably how she will be loaded most of the time. The prop is a mich. wheel vortex.<br />I would like to get a nice SS prop for her and I was thinking about getting the SS prop in a 17 pitch ... what do you guys think? I have read that you get higher wot rpm with the SS props so it should be about right for my rig?<br />Thanks Jon