Motor mount/prop issue?

[ntreder]

anyone.....

boat is a POLARKRAFT Kodiak 178 WT

I just repowered from a 2005 115 Merc carb to a 2010 150 Etec.
pre-repower:

Merc
RPM max 5000 out of 5250 with a max mph of 42.7 GPS with avg load
14x21 aluminum prop

Etec
prop 1 - 15x17 alum max rpm 6000 (over recommended max), max mph 47
prop 2 - 14.75x19 ss viper max rpm 5000, max mph 49.5
prop 3 is a 17 ss viper and just got today, will try it out and post results

question is I don't think the dealer mounted the motor exactly the same as the 115 as far as where the cavitation plate sits. Is there a general rule as to where that should be..

that 115 screamed, and I'd expect more out of the 150 etec. There also seems to be more spray in general coming from the back of the boat motor and sides (and I do understand that there is 80-90 more lbs in that new motor....

thanks!
one more thing, the dealer is getting me a 17 pitch stainless viper to try instead of the 19 pitch. But everything I've looked up online recommends for that boat and load calc...a 14.25x19....maybe this is all because the motor isn't mounted perfect...but you'd think dealer knows what they are doing

 

[SparkieBoat]

Re: Motor mount/prop issue?

the place where the fin attaches to your outboard, (whether you have a planing fin or not) should be at the water level when you are at WOT and trimmed out. you may need to jack the motor up some more if it is too low, also trim tabs can help "lift" the transom and counter the extra weight. I assume both motors are the same length shafts. once you jack the motor up the 19 pitch prop will probably get a good boost in RPMs and speed. general rule is cavitation plate should be about level with bottom of boat, but you can often raise it higher, which can produce a big benefit. I jack mine up till just before prop starts ventilating.

 

[ntreder]

Re: Motor mount/prop issue?

Yea, I have to examine that....

As far as the prop goes, the 19 pitch SS viper is only spinning 5000 even on the etec which is top ended at 5850 or so. So I believe 19 might be ok, but I think I may be pushing water. It is mounted on the first hole(out of 4 can go up 3 x .75 inches) and it does appear that the anti cavitation or ventilation plate is about 1 inch above the very bottom of the reverse chine hull. So it is a sharp v at the bottom...both shafts(previous and new) are the same standard 20". I do believe(I wish I would've looked more closely) that the old motor was mounted one hole up. I guess it can't hurt to try it out, and then experiment with both props I have on hand until I return one...the 19 and the 17 SS vipers. thanks for the input! If anyone else has a reverse chine aluminum hull, would you consider mounting it up higher since the bottome of the boat isn't flat there is more potential for water to slam into the plate?

 

[ntreder]

Re: Motor mount/prop issue?

tested out the 17 pitch SS viper prop.

Max RPM 5600-5800
Max MPH 48.5

It still seems that there is too much spray going on down there, I figure it won't hurt to try and raise it one hole and then test both props again.


I still need to examine the antiventilation/cavitation plate tomorrow when I have a driver in the boat with me.

 

[quackaddict1]

Re: Motor mount/prop issue?

The experience I have had with all three boats I have played with is that where the factory set it was to low in the water, I have no experience with your boat but I would be it is set up to low, especially with a SS prop that has good bite, you can run a motor higher than what most think.

I added a jack plate to a 16ft aluminum tub with a 28hp Johnson and I ended up moving the motor up 5 inches and picked up 4mph on the top end.

See my current prop question thread for the current setup I have been playing with... Same story

 

[ntreder]

Re: Motor mount/prop issue?

The experience I have had with all three boats I have played with is that where the factory set it was to low in the water, I have no experience with your boat but I would be it is set up to low, especially with a SS prop that has good bite, you can run a motor higher than what most think.

I added a jack plate to a 16ft aluminum tub with a 28hp Johnson and I ended up moving the motor up 5 inches and picked up 4mph on the top end.

See my current prop question thread for the current setup I have been playing with... Same story

thanks for the info! I'll report back what happens...hopefully tomorrow night or Fri morning.

 

[ntreder]

Re: Motor mount/prop issue?

Wanted to add another note for anyone who is thinking about jacking up there motor and haven't done it before....It is EASY.

I did my ETEC 150 in about 25 minutes. The top bolts come out, the bottom two (on the etec) actually have a slide hole so they just need to be loosened. I put the bottom of the motor on a contrete pad, and once everything was loose and bolts removed, I used my front wheel jack (started with it low to ground) and raised it up 12 cranks....pretty much perfectly lined up the next holes. Reapplyed sealant and then tightened up. Done! Will be testing my SS viper 17 and 19 pitch props tonight on the new height. Will post results.

 

[quackaddict1]

Re: Motor mount/prop issue?

I would bet money you will pick up RPM's, if one hole shows improvement try two, as long as it wont blow out or loose bite you will be just fine.

 

[SparkieBoat]

Re: Motor mount/prop issue?

yea keep going up until you get noticeable prop slippage (venting). when running WOT and trimmed out what level is your cav plate?? is it out of the water, or 2 inches under water???