Help with prop selection

Tristan.Jarvis

Recruit
Joined
Jun 8, 2012
Messages
3
Hello,

I am trying to find out what would be a great prop to purchase for our boat. We have a stern drive runabout that we use for 90% watersports, if were not towing (wakeboarding, knee boarding, or tubing) we are heading to the dock or have the anchor out and we are swiming. We are comfortable with our cruising speed if needed around 35 to 40 MPH on our small lakes that we utilize. Any faster is not practical if we have the kids or dogs around.

I am currently torn between some type of 4 blade or 5 Blade prop, due to increased non slipage, lift, turning slip properties and ability to hold wakeboarding speeds better. We do ride in smaller resivors that are not that deep. So I am not sure of stainless at this time. I am not sure what a good prop and pitch would be.

Our boat is a 2006 Larson Senza 186. It has a 4.3 GLE Volvo Penta 190 Hp, SX M Transom and SX M1 1.79 outdrive. The prop is a factory 3 Blade Alluminium 14.2 x 23.

Issues that I have noticed is anytime the boat is weighted down we have a hard time getting on a plane. This is significatly worse when we are towing with a lot of heavy passengers. We had 7 adults (Capacity 9 or 1400lbs) on the boat the other day witch translated to about 1200 Lbs + Tower boards Equipment ect. (Roughly 1350- 1400 Lbs) With that weight on board, the boat would pop me right out of the water on the wakeboard (195 lbs) or knee board but would strugle to get on a plane (I/O Trimmed all the way in). Once we were on a plane there was no issues other than having to give it fuel through the turns to stay on a plane at wakeboard speeds. The boat does walk around quite a bit with speed/ throtle control. That should soon be fixed with either ridesteady or perfect pass install.

When we had all the adults in the boat the other day we were riding about 450 Lbs in the bow. We had a significant bow rise issue/ hard to reach a plane. We are currently not looking to invest in tabs for the boat. I like the smart tab concept for some boats, but these will not work for us since the will reduce the wake for wakeboarding and we can not dissengage them manually, in that regard due to our swim platform. If we get the correct prop and still have an issue then I might consider a manual tab (Bennett) if needed to provide lift on the transom to help reach a plane. I would like to simplify driving for my significant other and others, though with out the need for the tabs. Any listing issues would be fixed with moving passengers.

We did some testing of the current prop today. From my research the WOT Max RPMS for this motor should be aprox 4200-4600. Are testing was done with almost glass/ 1' to 2' Rollers in the testing area. Times/ Speeds were from stopwatch and Gps in the boat. Load in boat was most regular gear, tower, 600 Lbs of passengers. Anywhere from this load to the load above (1400 LBS) would be an average load untill I talk my significant other into some type of ballast to increase the wake.

MAX RPMS untill planing 3000

Time to Plane
7.4, 7.8, 8.3, 7.8, 7.9, 7.6

WOT RPMS/ TOP SPEED Reached during that Run
4300 46.5
4300 47.4
4300 47
4300 46
43/44 48.3
4600 46.5

We were able on the last run to increase the RPMS but speed decreased with this trim level. It was hard to read the rpms but they were right over 4500-4600. Our test area was some what small on a harshly controlled speed zone lake.

Thank you in advance and we appriciate your help with this prop selection.
 

kmarine

Chief Petty Officer
Joined
Nov 5, 2010
Messages
591
Re: Help with wakeboarding prop selection

Re: Help with wakeboarding prop selection

as a wakeboarder and slalom skier I can simpathise with your concerns. If you go with a lower pitch prop, you will over rev at top speed. you could try a prop shop bringing your rpm and speed chart with you and see what they can do. On my old IO boat I went with a lower pitch prop and then added cupping to create more lift at take off. only concern reduce over reving at higher speeds. I also had the prop vented to allow exhaust gasses to escape in front of the prop at slower speeds alowing faster rpm gain to help speed up holeshot. As for adding perfect pass or ridesteady, I would prefer to upgrade to a inboard type or dual prop io boat. The cost of the system would control speed, however your ride expierience is far greater with a boat set up like this. The reason these boats have v8 engines is to provide low end tork as well as consistant speed control at plaining speed threshold. extrimely dificult to control with a v6 IO. Find a good prop guy. he can help. I use airmarine in chicago, dont know where you are at.
 

Tristan.Jarvis

Recruit
Joined
Jun 8, 2012
Messages
3
Re: Help with wakeboarding prop selection

Re: Help with wakeboarding prop selection

I do enjoy wakeboarding as one of my primary water sports. Our current boat will throw a decent wake for being an i/o. With the lakes we normally use it is hard to find glass like conditions to wakeboard. Wakeboarding is normally limited to mornings or evenings. We will then participate in other watersports or swiming. At this time I wakeboard and have a few friends who will as well. We are currently not looking for a sole wakeboarding boat. The significant other likes have the family orrientation of the runabout, ability to handel the chop on our lake and fuel savings. I understand you cant have the best of both worlds all the time but I am trying to maximize what I can. Also due to finacial situations we are going to have to stay with what we have now. In a few years if the kids 4 and 8 move into more sole wakeboarding or wakeboarding at all, then at that time we will consider upgrading to a used vdrive or inboard wakeboarding boat.

I have already justified the need for the ridesteady or perfect pass install. It gets to the point now of too much stress of even wanting to get behind the boat. Expecially after feeling like you gave someone a decent pull. Our boat gets on a plane at about 15/16 MPH now and we get a good wake anywhere between 18-22 it does change some.

I was thinking about your thoughts with the possible over reving. If we moved to the 4 blade we should drop 150 rpm alowing us to go to a 22 pitch off the bat. If we looked at the 4300 trimmed correctly we could move to a 21 adding another 200rpm putting at 4500 with a little over trimming taking us to 4600 and a lot to 4800. This would allow us to possibly over rev 200 rpm. With our minimum load in the boat. I do not know how accurate the analog stock rpm guage is as well. This could be countered by reading the electronic rpm read out on the perfect pass install and utilizing the rpm mode for cruising to maintain a safe rpm range. I dont know if the 21 with the 4 blade upgrade make a significant improvment? Would this be a safe pitch range or would you consider moving even more?

I have heard that the 4 blade will allow lower planing speed (Currently 15-16 MPH) more lift during holeshot, and better speed holding in the turns. What kind of impact will the 4 vs 5 blade have in our application during slow handle movment IE. backing of the boat?

Thanks
 

kmarine

Chief Petty Officer
Joined
Nov 5, 2010
Messages
591
Re: Help with wakeboarding prop selection

Re: Help with wakeboarding prop selection

a 4 or 5 blade prop will usiually manuver better in slow speed applications, they also are known to run smoother in large boat applications. as for fuel savings, in sking applications a v6 will have to work harder than a v8 with less throtle& more torque. my mb sport boss 210 with a 351 cu in engine uses less fuel than my old 18ft regal with a 4.3 as I am not nearly on the throtle like with my old boat. As for the perfect pass, maybe I am olod schooland find it nice , but expensive, I paid over $2000 for that option when I bought my boat. and seldom find it necessary with my current set up as my throtle does not wander much.
 
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