Need more gitty up

[FishnMike]

I have a 2008 Duckworth 195 Navigator Sport pushed by a F115 Yam slinging a 13 3/8 by 19" 3 blade alum. prop. Boat is 19.5 ft, alum., deep V, windsheild boat. Hull weight is about 1,550 lbs and on the water weight is about 2,600.

Boat runs great for most of the fishing I do with 2 to 4 people onboard. Boat planes well. Motor hits 6,000 RPM running about 38 mph. The one issue I have is when I take it out on the ocean during salmon season. Obviously have more weight on board then with a large ice chest, 4 downriggers, downrigger weights ,etc. If conditions are good, it still runs and planes well. Where I start encountering issues is when a swell starts running. Going against the swell, still not too bad but if I am running with the swell I have a heck of a time building RPM fast enough to push through the back of the wave so I end up wallowing along the back of the wave.

I would also like a little more stern lift to help bring my bow down in chopping conditions when i can't run all that fast. So overall I am thinking of going to a 4 blade to help with the stern lift and to give me more power to push through the backs of waves. Would going to a 17 pitch give me enough extra RPM or do I need to step down further?

Thanks,
Mike

 

[steelespike]

Speaking very basically.
If we calculate for slip it comes up 24%, very high.For now we have to assume either the tach is reading in error too high or perhaps the speed is in error low.
Is speed by gps? Is the prop in good condition?Your thoughts makes sense but when we know better about your actual numbers.The prop selection may be different though a 4 blade may still be a good idea.

 

[FishnMike]

24% would be very high. The speed is by GPS, two different units on board. Prop is in excellent condition. Is there a way to test the tach without just replacing?

By the way, the Yamaha performance bulletins for that motor on the same boat show pretty much the same numbers I have. My boat is probably heavier just to more crap and a kicker. http://yamahaoutboards.com/sites/def...rt-f115txr.pdf Although they were running a 17 pitch.

 

[steelespike]

You may be able to borrow a shop tach or get an induction tach to compare it to.
Knowing the Speed by gps simplifies things a little.
Also comparing to the test boat makes it obvious that that your rpm is very likely lower than indicated.
Your speed being approximately the same seems to indicate your rpm is actually low.
You still need to confirm the tach to be sure there isn't some strange anomaly going on
and so you know where your at with a new prop.

 

[FishnMike]

Ok, thanks for the suggestions Steelspike. I'll see if the local shop will let me borrow their tach and do some testing.

 

[steelespike]

Forgot to mention there is a selector switch on the back of your tach.Note its position and operate it a few times to clean the contacts.

 

[FishnMike]

Ok I'll try that too. Thanks again.