Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

[MuskyHunterDave]

Hello. . . . .<br />Well I finally got the new motor on the water and was able to get the WOT rpms.<br /><br />I am curious if the prop it came with is the proper one, as I need to buy a second so I have a spare, and if I am able to change the pitch to attain more speed, or is this the best scenario I can get.<br /><br />I have a 1969 ALL ALUMINUM 18' foot . . . 1/2 cuddy boat with a v'ed front leading to a relatively flat bottom.<br /><br />

<br /><br /><br />At WOT 5200 RPM I can achieve a max speed of 35mph. We used a gps for the speed reading.<br />The prop that came with the motor has the following number on the prop by the nut:<br />13 3/4 X 15<br />391198<br /><br />Dhadley said previously that you guys could calculate for proper prop to boat / motor off the WOT rpms.<br /><br />Thanks in advance for the assistance<br />Dave

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

ANother thing I was just thinking about that my be notable is, as you can see in the photo, the water line indicate she ride deep in the back. I at this time have a 3 battery system as well as #2 6 gallon tanks in the rear, but am planning on having a 30 gallon bow tank made to give me more fuel, and distribute the weight better on the boat.<br /><br />How will this affect things as far as changing the Wot - boat - motor calculation, or is it even an issue ????

 

[Dave Abrahamson]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Sounds like you're about 600rpm's on the low side. At 5200 WOT your lugging the motor. How is the setup? How high is the motor mounted on the transom? Is the AV plate (the one right above the prop) even with the bottom of the boat? That motor should be seeing 5800+ rpms for a long and happy life. FWIW my J90 that I used to have turned a 12 3/8 17p at about 5900rpm's.<br />The pros will be along shortly to help you more than I can. Good luck!<br /><br />Dave

 

[Dhadley]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Thats about 6-7% slip and I don't think thats right. The speed is probably close and the pitch is what its stamped so lets look at the tach. Are we sure its right? Is it a Teleflex brand?

 

[Dhadley]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Ooops! I must have the hiccups.........

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Hey. . . . Dhadley <br /><br />Here is the link to the tach I bought<br /> http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=4604730453&sspagename=STRK:MEWN:IT <br />Remember that was one of the ones I asked you about a few weeks back, and you said it would work.<br />It is set to the #4 setting, and idles around 900 RPm and WOT 5200 with the prop that came with the motor as stated before.<br /><br />Hiccups ??<br /><br />Thanks for the advise<br />Dave

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

So what is the slippage you talked about ??

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Hello. . . Dehadley<br /><br />Went out yesterday with a full boat of guys Large guys <br /><br />WOT dropped to 4900 due to the weight, and she still idles around 900<br /><br />Still waiting fo rsuggestions to last reply.<br /><br />Dave

 

[sycamore]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Musky, I have a 88hp Johnson on a 20' Sea Ark Jon Boat. It is 6' flat on the bottom in the back (8' beam) with a coast guard front. The boat rides high on the water. I carry 4 batteries, 2 trolling motors stored into 2 truck boxes, 3 anchors and the rest of the equipment. I just installed a new tach and here is what I have seen on GPS with 3 large fishermen:<br /><br />13" X 19 SS I turned 4900 RPM and 39MPH. <br />Got rid of that and put on a: 13 1/4" X 17 and turned 5300 RPM and 38 MPH. I am now getting a: <br />13 3/4" X 15 IN HOPES OF 5600 RPM and 36 MPH.<br /><br />I have played with the motor height but as I raised the motor I got some spray on my back and I lowered it back down.<br /><br />Hope this helps.

 

[Silvertip]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Propeller pitch (say 15 inches) is the amount of forward motion the propeller "theoretically" achieves in one revolution. However, because the prop operates in a liquid environment, it is not 100% efficient so some slippage is inevitable. 6-7% slip is not a realistic number meaning something is wrong. I believe the tach should be set on 6, not 4 (unless this is a non-standard tach).

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Well when I set the tach at 6 the rmps went through the ceiling.<br /><br />I messed with the settings ont he tach, and found that 4 gave me the 900 at idle, and figured that was what I needed. There is a link above showing the tach that dhadley said would work . . .?<br /><br />Dave

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Hey Dhadley . . . .<br /><br />You still around ?????????

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

I was under the impression that this motor had a 12 pole alternator, and the tach purchased was for such engines . . . . ?

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

How much of an issue is the weight displacement issue with most of the weight towards the rear of the boat ??

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

The cavitation plate is just ABove the bottom of the boat

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Sorry for all the info, but I am taking the day off, and have lots of time for the comp. <br /><br />Another question that has come to mind:<br /><br />I am new to the power trim, so how high is too high when trimming up at wot? I did notice the bow starting to bounce at higher trim setting, and simply trimed down as needed to stop the bouncing . . . .<br /><br />Dave

 

[Dhadley]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

The Faria stuff is notorious for being off. The tach setting should be on position 6 (12 pole) for your motor.

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

SO you are saying the tach is bad ????<br /><br />As I said, it hit the ceiling at wot and idles around 2400 on setting #6<br /><br />dave

 

[walleyehed]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Faria built for an I/O.....Hummmm...<br />I would say "6" too but 2400 at Idle isn't right..900 is pretty high too...700-750 would be better.<br />Sounds like a bad tach to me..

 

[MuskyHunterDave]

Re: Is this the Right PROP ??? 92 evin 90HP 18' Boat 5200 WOT @35mph

Wy are we so convinced, and saying the tach is bad when it seems to be operating fine. we are talking about 700 rpm (5200=now to 5900=needed) and couldn't that be attained from a different prop???<br /><br />Is there a test for the tach to assure it is working properly ???