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Going up on prop pitch need some thoughts

Old 10-28-2020, 03:16 PM
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Default Going up on prop pitch need some thoughts

So I'm running m6 race drives spinning IN 1.50 gear ratio nortech 43 super vee, I have a set of 18x32x18 hering 5 blades and I'm hitting 104mph at 5500 rpm and it'll go to 6000rpm trimmed more and maintain 104mph just more slip.higher trim then that and it loses speed. how much pitch can I go up to gain mph using higher pitched hering props? And if I switched to Merc props what's the equivalent pitch compared to hering. I have heard the mercs are slower.
I know there's more in her as it gets up to top speed very fast and is very torquey and I don't mind losing some rpm to gain top speed I'd be happy at 5000-5200

Last edited by beerock; 10-29-2020 at 12:57 PM.
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Old 10-29-2020, 12:02 AM
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If there is absolutely no change in speed between an engine speed of 5500 rpm and 6000 rpm then I would make sure that your speedometer is reading correct, check it with another resource such as your phone. Even with an increase in slip you should still be gaining mph. With that large of a gain in rpm you should be running close to 113 mph, assuming that you aren't gaining any slip, even with a 3% increase in slip you should be running around 110. Right now you are going from 6% slip to 14% which doesn't make any sense, especially since you are running surface drives. If you are trimming the boat out to get your increase in rpm then that is where your slip is coming from but if you aren't trimming up the drives excessively then something is wrong, you should be gaining a decent amount of speed. As for props herrings are normally one of the fastest props out there. You could try moving up to a 33 or 34 pitch prop and see if those help. You should gain around 3 and 6 mph respectively, asssuming that the boat can still spin the props.
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Old 10-29-2020, 12:12 AM
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Originally Posted by Andrew56 View Post
If there is absolutely no change in speed between an engine speed of 5500 rpm and 6000 rpm then I would make sure that your speedometer is reading correct, check it with another resource such as your phone. Even with an increase in slip you should still be gaining mph. With that large of a gain in rpm you should be running close to 113 mph, assuming that you aren't gaining any slip, even with a 3% increase in slip you should be running around 110. Right now you are going from 6% slip to 14% which doesn't make any sense, especially since you are running surface drives. If you are trimming the boat out to get your increase in rpm then that is where your slip is coming from but if you aren't trimming up the drives excessively then something is wrong, you should be gaining a decent amount of speed. As for props herrings are normally one of the fastest props out there. You could try moving up to a 33 or 34 pitch prop and see if those help. You should gain around 3 and 6 mph respectively, asssuming that the boat can still spin the props.
I edited it, 6000 trimmed out more... And yes my gosh says 104 but I walked another guy's boat that says he does 105 on gps.. I don't trust GPS I've had gps in other boats and same **** 2 read different than my phone. In other words all 3 had different speeds..

With the 18x32x18 the boat has tons of pull and gets up to top speed very quick.. it is a dog out of the whole have to spin 3-4000 super cavitating them to get on plane which is normal. Once on plane it'll stay on plane down to 30-35mph and once on plane the blades grab and rpms drop.

I feel it could go up in pitch but I'm not sure how much is too much. I also have a smaller pullley for race gas and I'm sure the mph gain will be just as apparent if I swapped and with more pitch . I have to get props anyway so I figured I'd mess with pitch.. not sure I should mess with diameter
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Old 10-29-2020, 02:38 AM
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What engines??? and what rpm is max hp?? If they are fine at 6000rpms, then you really don't want to go up in pitch.
Maybe some increased rake to reduce slip% and increase speed when you trim up
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Old 10-29-2020, 10:50 AM
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As Griff asked what is the max HP rpm? Prop towards that. Rather than adding pitch in this scenario I might suggest you increase prop diameter 1/2" to maybe 1". The increased diameter will offer a little more bite when up on plane at those speeds to take advantage of the extra 500 rpm you were extracting. Rake, as suggested by Griff, might not be a bad idea either.
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Old 10-29-2020, 11:35 AM
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Originally Posted by Griff View Post
What engines??? and what rpm is max hp?? If they are fine at 6000rpms, then you really don't want to go up in pitch.
Maybe some increased rake to reduce slip% and increase speed when you trim up
Max hp is @6000 rpm 1132hp 991tq @5500 1095hp 1046tq its only 37hp less @5500rpm but has +55tq

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Old 10-29-2020, 11:45 AM
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I would try dropping down to a 32 pitch prop. This should allow you to turn the needed rpm without trimming up the drives to do so. Right now it sounds like you are just trimming the drives up too far which is causing the props not be in the water enough, inturn giving an increase in slip and rpm but no mph gain. I have a set of 32 pitch herrings on my 42 cigarette tiger which allows me to run 105 at a little over 6000 rpm. I have IMCO scx drives so I should be seeing more slip than you normally would. I think your boat is simply over propped with the 34's.
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Old 10-29-2020, 11:51 AM
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Originally Posted by Andrew56 View Post
I would try dropping down to a 32 pitch prop. This should allow you to turn the needed rpm without trimming up the drives to do so. Right now it sounds like you are just trimming the drives up too far which is causing the props not be in the water enough, inturn giving an increase in slip and rpm but no mph gain. I have a set of 32 pitch herrings on my 42 cigarette tiger which allows me to run 105 at a little over 6000 rpm. I have IMCO scx drives so I should be seeing more slip than you normally would. I think your boat is simply over propped with the 34's.
Re read my prop size.. I'm running 18x32x18
im also running low boost I have pulleys for high boost which will also gain if I go up on pitch or rake. Thing is I'm posting here first because testing herings isn't cheap at all so I already have a slight idea of what to test out just want to hear opinions and thoughts from others and then I'll make my own decision based off of others as well or not at all


Last edited by beerock; 10-29-2020 at 11:55 AM.
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Griff (10-29-2020)
Old 10-29-2020, 11:55 AM
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Originally Posted by beerock View Post
Max hp is @6000 rpm 1132hp 991tq @5500 1095hp 1046tq its only 37hp less @5500rpm but has +55tq
How much does your boat weigh? I'm running 945 horsepower with IMCO scx's and getting the same speeds you are. If we are similar in weight, my tiger weighs around 10,500 lbs, then you should be easily into the mid to high 110's. Again I'm thinking there may be something off with your speedo. A truely accurate measurement from something like a v-box or dragy would answer some of our questions.
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Old 10-29-2020, 11:57 AM
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Originally Posted by beerock View Post
Re read my prop size.. I'm running 18x32x18
It does help when I use the correct information. One of the only other things I can think of would be that your props could be too large in diameter. Its possible that the 18 inch props just have too much drag in the water to spin them properly.
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