21 Pitch seems too much, Should I shave the prop?

[Chevyboy454]

So after I spun the hub out of my beautifull stainless prop, I called a local marine shop and he told me I should be using a 21 pitch on my setup. (I think it's because he wanted a sale and didn't have any 19's in stock.) With the 21 My boat feels like a dog getting out of the water and my top end at max throttle is only 60 kph, (Had the gps on board that day) I don't know what I was running before with the 19 but I can say it sure doesn't get out of the water nicely anymore and it feels slower. Should I take 1/4 inch off the edges? Going on Vacation Saturday and I don't have time or the extra cash to buy another prop. It's one of those fancy ones with the rubber hub that's "guaranteed for life" Came with all the trust washers and stuff. Went on real good, I did have to modify the little fin thing as the prop was hitting it. Any Advice, I see I'm not the only guy that wouldn't mind swapping a 21 for a 19 on the net. If I can trim it and save some cash that would be cool. If not I guess I'll have to wait for more cash and deal with it over my vacation.

Cheers Rick.

 

[BSAFlash]

Re: 21 Pitch seems too much, Should I shave the prop?

It is more about revs than speed...
Your engine should be able to run to or just below its max revs. If it is able to over run the redline you have a problem!
I spoke to a Volvo tech at the Sydney Boatshow last Friday, he suggested my pros may be 2 sizes over... (As supplied by Doral and tested by the ... that commissioned her) but the boat will be slower when I change to the correct prop!
I must admit I like being able to over take twin rig trailer boats :redface:
I tend to avoid the fast jump from stationary to warp drive these days so I'm hopefully not putting too much load on the engines or drives.

My highly modified Mercs used to strip the rubber centre hubs every season or so... that and the need for speed was the reason for changing to solid centre surface piercing props... Just make sure you don't hit anything in the water, instead of sacrificing the rubber hub you sacrifice your gearbox:facepalm:

 

[kenmyfam]

Re: 21 Pitch seems too much, Should I shave the prop?

Rick, buy an old 19" aluminum prop and you can play around with it by "porting it" and tuning the diameter and cupping. remember taking too much off then becomes a welding adjustment. I have a 19" on my set up and it is ported as well. I have "fine tuned" the cupping a little as well. Entire set up needs to be looked at for peak efficiency as well though. Have to make sure the blades are even and balanced as well.
Enjoy your vacation. I will be on vacation next week.

 

[Chevyboy454]

Re: 21 Pitch seems too much, Should I shave the prop?

Just popped in at the house to grab some tools, the 21 is killing me in every way. I grabbed the 19 and plan to shave down the 21 to match it. I went through 5 gallons going out only once on pittock from centre of lake to dam and up to the first bridge and back to camp = 5 gallons. That's 5 times more gas then I ever used with the 19, it has to work like a bugger to get on step and when on step its at max throttle and as I said befre it only hits about 55 60 kph. I know it was a heck of a lot faster before and it's never chewed through gas like this before. Prop came pre ported so I wont need to do that, I will let you guys know how I make out when I'm back.

Cheers! Rick.

Vacation ROCKS!

 

[kenmyfam]

Re: 21 Pitch seems too much, Should I shave the prop?

Good Luck. Photos of the porting would be interesting. Full cupped 17" would be fun as well to try.

 

[Chevyboy454]

Re: 21 Pitch seems too much, Should I shave the prop?

Well, I took the tools out to camp as well as my 19 for reference. Made a cardboard template of the blade on the 19 and held it up against the 21. The pitch is too great to do anything with, I did shave 1/4 inch off the top of the blades and it seemed to increase my hole shot by about 2 seconds but still no where near what I had. Top speed increased by 2 kph which is not even worth mentioning. Popped on the 17 I picked up for cheap as a "get out of trouble prop" and it's not something I want to do again, Engine just reves out like crazy, way too small. Good enough to get me back to shore but not something I would want to use regularly. I'm in the process of looking at something a little bigger, the 165 is not much for room and after spending some time on my brothers boat and seeing all the other boats out I have decided we are going to need a 19 or so. Found many on the internet for free that need various things, so I may pick up one of those and work on it over the winter. Got my eye on a Renken right now, 19 foot, I/O 3.0, its all there but apparently the block is cracked. Think I'm going to go with an I/O, getting tired of the whole outboard thing never was big on 2 strokes and a 4 stroke is too pricey for me. Anywho here are some pics I took out a Big Chief yesterday of my Brothers boat.

Cheers Rick.