went from 3 to 4 blade made things worse

[ozarkmed]

Hey guys, I have a 2007 glastron 18ft F&S with 3.0 Volvo-Penta and SX outdrive. 3 batteries in back also. WOT rpm is 4200-4600. It came stock with a 3 blade alum 14.25 X 21 which was great at wot and ran 39mph (gps) at 4600 rpm but sucked off the line or when I had any more that two people on board. Didn't really have any handling issues as boat is very stable running in rough water at wot. My average day is with 3 ppl on board and pulling skier maybe a third of the time and cooler and snacks.

Switched to a 14.5 X 19 which gave me great hole shot and mid range power, but ran 34 mph and 5,000 rpm at wot. Seemed to handle the same, but slower.

So, I wanted one prop that would give me more grunt off the line and maybe only loose a couple of mph and not over rev like the 19 pitch was doing.

After lurking here and elsewhere and reading most everything I could I ordered a Michigan Wheel Apollo 4 blade stainless 14.25 X 20. Installed and ran it yesterday with 3 ppl on board and approx 18 gal of gas. Water was rough (1-2 ft) and choppy due to holiday traffic and wind, but found some protected calmer areas to test.

It sucked and here's why:
1. hole shot slightly better than 21 pitch, but not as good as 19pitch 3 blade. Not what I wanted, but I could live with that if not for the other issues.
2. ran 33mph at 4150 rpms......so I'm not near my 4600 goal and speed sucks
3. Boat cornered nice and tight and seemed to hold rpms and speed better in tight turns in smooth water, but was very unstable at top end in the rough water and started bouncing severely from side to side (chine walking?) and we dang near crashed. I've driven it many times faster than this in rougher water than this and never had that happen.
4. And strangely, the boat tended to porpoise at any speed and no matter the trim. In fact, after a few minutes I just gave up and left the trim in the full down.

So, first off, I've got a brand new slightly wet Apollo 4 blade stainless for sale.
I'm very concerned about buying another 4 blade. Was thinking about getting a stainless 4 blade 19 pitch, but I'm thinking that "stern lift" is not healthy for my boat. Is my hull one that may not benefit from a 4 blade?
Should I just get a good stainless 3 blade 19 pitch and be careful about the rpms?

No "prop shops" anywhere close to me. But being as I have 3 props in my garage right now, I may open one up.

Your thoughts would be appreciated.

 

[chriscraft254]

Re: went from 3 to 4 blade made things worse

When you say trim, do you mean motor trim or trim tabs. Sounds like you need to invest in some trim tabs and put the 3 blade prop you had on to begin with.

 

[ozarkmed]

Re: went from 3 to 4 blade made things worse

I hadn't considered trim tabs. I haven't seen many in use in this part of the country. Only recently read some about them here on this forum. It's something I'll certainly consider. Thanks.

 

[John_S]

Re: went from 3 to 4 blade made things worse

Were all three props run with the same load? Based on the 1st two, I wouldn't expect that amount of rpm drop with the 20P 4 blade. From the high speed performance of the 4 blade, sounds like it is providing more stearn lift than needed. My guess would be is that your hull has a "wider" v (less deadrise) than typical. A 3.0L in a 18'er probably doesn't "squat" much at the stearn, either.

Having one prop that does it all, especially with a 3.0L engine, is probably optomistic. Use the 19P" for skiing and water toys, and more people (load) days. Switch to the 21P for the light load days. If you are trailering, swapping props is not that big of deal.

A set of smart tabs will allow quicker planning and help control any high speed chine walk or porpusing. I'd consider those if you have a transom that can accomedate the installation. If you boat allot in "big" water where it gets rough, you may want to consider the more expensive manual control tabs.

 

[ozarkmed]

Re: went from 3 to 4 blade made things worse

Yes, all three runs were done with same basic load and I'm confused as well with the performance of the 4 blade. I put my 19p back on for now and will probably put the 21p on in a few wks for fishing (longer runs at speed with maybe one other person).

 

[wellcraft19]

Re: went from 3 to 4 blade made things worse

As you can read in my separate thread (http://forums.iboats.com/showthread.php?t=493617), I am not super happy either with my new 4-blade, but that has to do with me dropping from a 19" to a 17" pitch when adding one blade (there is no 18"). Resulted in me being horribly under propped. Should have stayed 19" pitch even with the 4-blade, against common sense, or recommendations..
Part from that, good grip, and the Solas seems to be of good quality.

 

[Riegfrghtl]

Re: went from 3 to 4 blade made things worse

I have a 1972 Cruisers, Inc. with a Mercruiser 888. I originally had a Michigan 15 1/2 X 19p 3 blade prop on it. Performance was fair. Wot rpms were around 3800 (3800 to 4200 is manf. range for motor) with speed at 35 mph. My boat is fairly heavy and I usually have 40 gals of fuel and 3 to 4 people on board. Last year I added smart tabs and boat jumps on plane and handling has improved immensely. At the end of last year tested and then bought a 4 blade 14 1/2 X 18 Michigan vortex prop. All the props I have are aluminum. Hole shot improved and was able to get 4000 rpms after trimming. Speed dropped to 33 mph (gps). Was able to plane at much lower speeds. Thought it was a nice set up with the 4 blades and smart tabs. Could live with the slower top speed. The problem I had with the 4 blade was a ventilation issue between 2000-2500 rpms. My mechanic and I were unable to figure the cause for this problem. A couple weeks ago I borrowed a mercury 3 blade prop from my marina and it was a 15 x 17p alum. The performance difference has been amazing. Its like some dropped a big block in my boat. Boat jumps on plane, hits 4200 rpms with out trimming and now tops out at 41 mph (gps). Hit the throttle at 2500 rpms and it feels as though nitrous kicked in. Speed in mph were a little slower from 1000 to 3500 pms, but drastically improved from 3500 to 4200 rpms. Also the ventilation issue I had with the 4 blade is now gone. I bought the prop and love it. My point being is it took a year and some trial and error to find the set up that I was happy with. A little lower pitch allowed my motor to run at the proper rpms and at the upper end the motor isn't struggling to push the boat through the water. Just a thought!

Tim