New Member, New Toon, Prop Question

[bevans]

Hello all,
Recently purchased my first toon, i boat in NE Oklahoma. Sold my 1978 Chris Craft inboard to get more room for a growing family. I have really enjoyed reading the posts, lots of info and knowledge shared.

My "new" boat is a 1998 21' Voyager Tritoon, it has a 120 Merc Force. So far i love it, it needs some interior work, but the boat seems to have good bones and my wife and i have already been enjoying it!

I got it out for the first time with a GPS. The boat topped out about 18MPH. Plenty of speed for me, but seemed low from what i have read. I had way too many RPMS, i accidentally got it past the 6K mark once passing a barge on a river (max on engine is 5250). The prop that came on the boat is a 14x13. Anyone got a similar set up i could compare it to (RPM/MPH at WOT)? I figure id normally cruise 16ish, and i figure if i can dial in the prop i could save on some fuel and the engine working hard.

Thanks for the help!

[HandymanHerb]

Welcome, you need a new prop, my 50 will do 17 GPS, so you should be doing better than 18 for sure, I let someone with an engine your size kick in with a prop size

[dockholiday]

Welcome
Was the prop still pulling when you hit the 6k rpm? Guess what I am saying was it totally trimmed out and may have lost the bite on the water. 13 should be about right, but you might could handle a 15. A 21ft tritoon with a 115 (know yours is a 120) should at least be in the 25mph range maybe to the low 30's, providing the motor is running properly and the toons are clean. For comparison I have 30 more hp, but 3ft more boat and weight and I get 40mph. I do have the strakes so probably back out a couple of mph for those. If you are running an alum prop your boat probably warrants a ss prop. May not want to spend the money but bet a 14p enertia would be good on your boat.
doc

[lakerunner696]

Welcome and where do you toon?

[bevans]

Lake Skiatook mostly. I heard Tenkiller was hurting with the flooding, hope all is okay there.

[bevans]

Welcome
Was the prop still pulling when you hit the 6k rpm? Guess what I am saying was it totally trimmed out and may have lost the bite on the water. 13 should be about right, but you might could handle a 15. A 21ft tritoon with a 115 (know yours is a 120) should at least be in the 25mph range maybe to the low 30's, providing the motor is running properly and the toons are clean. For comparison I have 30 more hp, but 3ft more boat and weight and I get 40mph. I do have the strakes so probably back out a couple of mph for those. If you are running an alum prop your boat probably warrants a ss prop. May not want to spend the money but bet a 14p enertia would be good on your boat.
doc

Welcome

The prop was not having any cavitation like symptoms, it was seemed to get plenty of bite. The revs were smooth and consistent. There was very little if any trim. The trim didnt seem to make all that much difference.

Can trim make a big difference on pontoons?

[mike]

Welcome, I am always on the low end of the RPM range, I will check my prop tonight and let you know what I am running! Do you have two or three logs?

[bevans]

yes, it is a tritoon

[ROLAND]

A 21ft tritoon with a 115 (know yours is a 120) should at least be in the 25mph range maybe to the low 30's, providing the motor is running properly and the toons are clean. For comparison I have 30 more hp, but 3ft more boat and weight and I get 40mph. doc

Welcome

The prop was not having any cavitation like symptoms, it was seemed to get plenty of bite. The revs were smooth and consistent. There was very little if any trim. The trim didnt seem to make all that much difference.

Can trim make a big difference on pontoons?

first off.. welcome to the club.. you're right, there is a great group of knowledgable pontoon enthusiasts on here and I have to tell you these guys were instrumental in helping me get my prop issue lined out. Dealer over propped me, I thought that since I was running much lower rpm's but still getting close to the same speed I had been getting with my old prop, that I was good to go, when some of the boys here informed me that my motor was actually lugging or working too hard. I contacted Yamaha and their rep confirmed what the guys on this forum told me. For comparison, I have a 75 4-stroke on a 20 footer and under ideal conditions with just me and the wife on board I get 23 to 25 mph max... and to answer your question about trim making a difference, I know when I trim out to the "sweet spot", boat seems to run smoother and with a "little' more pep...

[bevans]

Got a new prop today, had a 13.5x15 put on. took the boat out and had the right rpm (5100ish) and much better speed (28mph on the gps). Now i can comfortably cruise at 20. The prop was totally the issue. Hopefully this info will help someone out down the road.

[dockholiday]

Got a new prop today, had a 13.5x15 put on. took the boat out and had the right rpm (5100ish) and much better speed (28mph on the gps). Now i can comfortably cruise at 20. The prop was totally the issue. Hopefully this info will help someone out down the road.

Yep it is amazing how off a lot of props are in pitch. If someone buys a boat an really don't have anything to compare to they just leave it as is. Even seen some dealers that should be in the know outfit with whatever is handy at the time. The bad thing the owners may ride around for over 10years with it.

doc