Bjhinson

My need for advice is probably a bit out of the ordinary for this site, but here goes. I run a Contender 32ST twin stepped center console fishing boat with twin 300 mercury verados and have a prop dilemma. I have tried 21" Tempest +, 23" tempest +, and 23" mirage plus. I'm currently running the 21" tempest +, but I'm not completely satisfied. The mfg. Recommended max rpms are 6400 and I can just barely achieve this with a full load running against the current and wind. At the end of a tournament day when I empty my livewells (80 gallons approximate) and have burnt off 75 to 100 gallons of fuel I've seen as high as 6700 rpm. The 23 mirages can turn to 6100 with a medium load and the 23 tempests can turn to about 6000 with a medium load. So...I feel like I'm stuck in the middle and leaving both performance and economy on the table. Even though 6000 rpm is within tolerance, the boat doesn't feel as good and the throttle response drops off quite a bit. The motors feel best turning max rpm. Now for my performance with the 21 tempests: slow cruise at 4200 - 4250 = 40 mph, normal cruise at 4700 - 4750 = 46 - 47 mph, and WOT at 6350 - 6400 = 63 - 66 mph (these are all loaded numbers and vary with wind and current). With a half load I've seen as high as 69.4 mph at around 6700 rpm. I have gotten the mirage 23s up to around 68 mph at around 6250 rpms with a light to medium load. I've never gotten the 23 tempests over 6100 rpms or 64 mph. Not sure why the 23 mirages perform better than the 23 tempests other than to say they have about 500 hours on them and both sets of tempests are under 100 hours, mirages are probably worn a bit.

My question is, I want to increase cruise speed and top end while still turning at or near max rpm (6400). Can lab finishing either my 23 mirages or 23 tempests get me 300 rpms? Is there another prop I should try, lab finished or stock? The engines seem to be mounted at the perfect height, the av plates are above the flow of water at cruise speed. I haven't noticed any cavitation with any of the props even in rough water, but the mirages had the least amount of available trim range before losing speed. Any help is appreciated.

Thanks.

Bjhinson

One more thing, Should I try a 4blade prop? This boat, with the steps, already runs very flat. Any suggestions to 3 blade vs 4 blade to consider in conjunction with the above info?

A.O. Razor

Ok, not a prop guru
But a Revolution 4 should give you better midrange. That is usually the case when adding blades. A non-labbed 21 should take you down about 200-300 rpm compared to a 21 Mirage+, and maybe a bit more compared to your Tempest+ 21. A labbed Rev4 23 could be the ticket.

bbladesprops

First, it is important to remember how important weight and water conditions effect boats. Certain boats styles will be effect more so than others by these variables. OB V-bottom boats realize the largest losses in performance from condition changes as compared to higher HP stern drive boats or air entrapment hulls. All this means is you can't expect the boat to do the same with a large load difference or current change.

I agree that the Revolution 4 is a great option on your boat. These props enhance mid range cruise speed and efficiency as well as maintain performance with load changes better than 3 blade props. However, the Rev 4's may be slightly slower on the top end.

Looking at your numbers, I would suggest Labbing the 23 Mirage + props to the correct recipe if speed is still the biggest concern. Also, the 23 will have better cruise than the 21's. Also, the M+ family is more responsive to the Lab process.

If you would like to discuss this in depth, call us anytime.

Brett