MikeH Posted October 29, 2020 Report Share Posted October 29, 2020 I am running a Powertech OFX4 23P on a 2008 21' MA with a 250 HPDI . I have seen 62mph at 5800 - 5900 RPMs (my recollection as to speed is correct but my recollection as to RPMs might be wrong). However, with a full load - 60 gallons of gas, cooler filled with drinks and ice, back center well full of water, 2 people on board, I am only getting 4600 RPMs and a max speed of 51 mph. Engine is running fine, my mechanic says it is running great with great compression, so I am confident it isn't an engine issue. I have only had the boat for 2 years and I haven't bothered until now to get the boat dialed in. I would say my current prop results in average hole shot, great mid range speed, and MPH always exceeding RPMs. I have read great things about the Bravo FS which is for four strokes. The Bravo XS seems to be what would work best for my 2 stroke HPDI. Does anyone have recommendations for what pitch would work best with my setup? Your suggestions would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
Lap it Up Posted October 29, 2020 Report Share Posted October 29, 2020 17 minutes ago, MikeH said: I am only getting 4600 RPMs and a max speed of 51 mph. Is this at full throttle and trimmed out? If you are losing that much RPM just from from weight then you have an issue. I have a 21MA also but with less power (2.6L 175). The 21MA carries load very well. I can run heavy or light and i don't lose anywhere near that kind of MPH or RPM. I have not run a Bravo but i know they are a great prop for bow lift and grip. Im sure others will chime in that have a big block like yours. Quote Link to comment Share on other sites More sharing options...
MikeH Posted October 29, 2020 Author Report Share Posted October 29, 2020 Lap It Up, Yes, this is at full throttle, trim tabs up, and trimmed up. I think I saw 4800 RPMs at 50 - 51 mph last week. Quote Link to comment Share on other sites More sharing options...
HoneyB Posted October 29, 2020 Report Share Posted October 29, 2020 IF your max rpm is 5800 now you are really pretty close on pitch. I would think a diffrent prop might help keep the boat up out of they water when you add weight. I would think you could spin about any prop in 21 pitch and have good results. 250 is a lot of horses I do not think you need to go down in pitch just to run with some folks in the boat. Try the Bravo1 fs the Yamaha HS4 or the Rev4 . They all seem to be very nice props. Quote Link to comment Share on other sites More sharing options...
mulligan Posted October 29, 2020 Report Share Posted October 29, 2020 I have different boat but same motor and have run both OFX and Bravo. The OFX was a 22 and ran close to 6k and the Bravo was a 23 and ran about the same RPM. The Bravo was a worked FS. I also ran a stock 25 Bravo XS to about 5600 if I recall. Quote Link to comment Share on other sites More sharing options...
jh141 Posted October 29, 2020 Report Share Posted October 29, 2020 The Bravo 1 FS is a difficult call. Mercury recommends adding pitch when switching to a Bravo 1. I went from a Turbo FX 22 pitch three blade that run pretty close to square to the end to a Bravo 1 FS 23.5 pitch and it runs 3.5 mph faster than rpm at the end. All other prop manufactures say "take away" 1 to 2 numbers when going from a three blade to a four blade. By considering your current loaded numbers you have to much pitch in your current prop. 4800 rpms says way to much pitch. I agree with Lap It Up. Something does not seem right with your numbers from lite to loaded. I would recheck all those numbers before taking any steps toward changing. I run a SHO four stroke on a 22 TRS so my exact setup will not help you, just the differences. Quote Link to comment Share on other sites More sharing options...
Lap it Up Posted October 29, 2020 Report Share Posted October 29, 2020 1 hour ago, MikeH said: Lap It Up, Yes, this is at full throttle, trim tabs up, and trimmed up. I think I saw 4800 RPMs at 50 - 51 mph last week. Sounds like you are down a cylinder at WOT. No reason to lose 1000 RPM's by just filling the tank and one well. Like i said... I have the same boat and don't lose much RPM at all regardless of load. You are possibly losing a coil or Injector at WOT. Or maybe junk in the VST. Quote Link to comment Share on other sites More sharing options...
HoneyB Posted October 29, 2020 Report Share Posted October 29, 2020 I did not read you title clearly the first go round. Sorry to muddy the water with talk of the other props. When I mentioned staying at a 21 bravo that is assuming your max rpm is at 5800 is correct. If you try a 21 pitch bravo you will likely bump 6000 to 6100rpm. If you move up in pitch as suggested by mercury( but when moving from there higher end props which as the tempest plus and the like) you may still not be happy when loaded. Quote Link to comment Share on other sites More sharing options...
Capt. Troy Posted October 29, 2020 Report Share Posted October 29, 2020 3 hours ago, MikeH said: I am running a Powertech OFX4 23P on a 2008 21' MA with a 250 HPDI . I have seen 62mph at 5800 - 5900 RPMs (my recollection as to speed is correct but my recollection as to RPMs might be wrong). However, with a full load - 60 gallons of gas, cooler filled with drinks and ice, back center well full of water, 2 people on board, I am only getting 4600 RPMs and a max speed of 51 mph. Engine is running fine, my mechanic says it is running great with great compression, so I am confident it isn't an engine issue. I have only had the boat for 2 years and I haven't bothered until now to get the boat dialed in. I would say my current prop results in average hole shot, great mid range speed, and MPH always exceeding RPMs. I have read great things about the Bravo FS which is for four strokes. The Bravo XS seems to be what would work best for my 2 stroke HPDI. Does anyone have recommendations for what pitch would work best with my setup? Your suggestions would be greatly appreciated. I don't see how you can turn those rpms with the OFX4 23. I have had 3 250's with OFX4 21on my current boat. Hard to imagine turning the RPM listed. The speed, yes light. I have seen 62 mph and my boat is never light for the most part. Runs about the same with the SHO vs the HPDI. SHO a tad faster You got something not right with the engine. Load ain't gonna drop you that many rpms. I can run fully loaded with 4 on board and all my gear for charter 58 MPH at 5800 RPM with the 250 SHO I have run a bunch of props on this hull. The OFX4 21 IMHO is the prop for this boat. It puts it on rails and brings tons of lift. Quote Link to comment Share on other sites More sharing options...
HoneyB Posted October 29, 2020 Report Share Posted October 29, 2020 The numbers seem off somewhere for sure. 21 to 23 should light you boat up behind a 250. What condition is the prop in? I do not think the hub is slipping you should feel that loaded or not. Surly the blades are not worn down and chewed up? I’m betting not but can’t see it from here:). Does anyone u know have a prop of any kind on a similar engine? All data is good to see if you see the same drop off with weight added. Quote Link to comment Share on other sites More sharing options...
Capt. Troy Posted October 29, 2020 Report Share Posted October 29, 2020 I am confused. 21 MA owner since 1999. New boat 2010 with new engine a few months ago. The 3rd engine on this 2010 hull and all 250 HP, the first was a 250 HPDI and now the SHO for the second time. Your numbers are not adding up! Call Marcus at Power Tech and speak with him. You have to have something else going on by your discription Quote Link to comment Share on other sites More sharing options...
redzone1 Posted October 29, 2020 Report Share Posted October 29, 2020 Seems like you may have a fouled spark plug or two......I know your mechanic says good compression across all 6, but are all 6 firing? Quote Link to comment Share on other sites More sharing options...
geeviam Posted October 30, 2020 Report Share Posted October 30, 2020 What about fuel restriction? I have had similar problems with a perfectly good engine, but the Anti-Siphon Valve on the fuel tank was sticking and choking off fuel flow to the motor. Fuel flow restriction can also occur when the vent on the tank has a blockage, and can't breathe like it should. Dirty fuel filter? Bad primer bulb (or installed backwards?). Just throwing in some things to check. I'm no expert, but I did stay at a Holiday Inn Express once or twice. 😉 1 Quote Link to comment Share on other sites More sharing options...
Capt. Troy Posted October 30, 2020 Report Share Posted October 30, 2020 57 minutes ago, geeviam said: What about fuel restriction? I have had similar problems with a perfectly good engine, but the Anti-Siphon Valve on the fuel tank was sticking and choking off fuel flow to the motor. Fuel flow restriction can also occur when the vent on the tank has a blockage, and can't breathe like it should. Dirty fuel filter? Bad primer bulb (or installed backwards?). Just throwing in some things to check. I'm no expert, but I did stay at a Holiday Inn Express once or twice. 😉 You better have none of the above! Lean that engine it will grenade! I will promise with same prop the additional load ain't no way dropping RPM and speed that much. EDIT to add your remark "I would say my current prop results in average hole shot, great mid range speed, and MPH always exceeding RPMs." Running better than square is a indication of being over propped. Proceed with caution! 1 Quote Link to comment Share on other sites More sharing options...
MikeH Posted October 30, 2020 Author Report Share Posted October 30, 2020 Thank you all so much for your time and expertise. I love this forum! I called my mechanic (Lou Baquero at Advantage Boatworks - he is the best) and he agrees that the problem is not being over-propped, but some issue with the engine. According to Lou (and you guys) the problem is most likely a coil issue, a clogged injector, a spark plug issue, or a problem with the stator. He said that if I at one time was getting a max RPM of 5800 with a light load, a heavy load should not reduce the RPMs down any further than 5400 RPMs, max, and probably not even by that many RPMs. I agree with Troy that Powertech vs. Powertech, it appears the 21 pitch would be better than the 23 pitch I am currently running. I will be bringing my boat into Advantage Boatworks next wweek and will let you all know what the problem was once it is fixed. Thanks again! Mike 2 Quote Link to comment Share on other sites More sharing options...
mulligan Posted October 31, 2020 Report Share Posted October 31, 2020 Advantage Boatworks in Tampa? Quote Link to comment Share on other sites More sharing options...
MikeH Posted October 31, 2020 Author Report Share Posted October 31, 2020 Mulligan, Yes, Advantage Boatworks in Tampa. Quote Link to comment Share on other sites More sharing options...
MikeH Posted February 27, 2021 Author Report Share Posted February 27, 2021 My mechanic did not find any problems with the engine. Just as a precaution, he cleaned more than one of the filters, even though he said they looked fine. He ran the boat and was able to get 5800 RPMs. So, the good news is there is no engine problem. The only thing I can think of is that I wasn't raising the jackplate more than at the "2" mark, and maybe I wasn't trimming the engine high enough. Maybe it was just user error. Regardless, I spoke with Marcus at PowerTech and agreed with Captain Troy that the OFX4 21 pitch, ported 3/8", is the prop for my boat/motor. I purchased one through Admiral C & B Propeller in Tampa, and although I have had it out only one time since then, I can tell you it works like a charm. Definitely much better hole shot and I was able to get a max of 6000 RPMs at 61 mph. Thank you all for your insight and great advice, especially Captain Troy! Quote Link to comment Share on other sites More sharing options...
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