Go Back  The Hull Truth - Boating and Fishing Forum > BOATING FORUMS > The Boating Forum
Reload this Page >

Is it possible to increase speed while decreasing pitch?

Notices
The Boating Forum

Is it possible to increase speed while decreasing pitch?

Old 08-08-2018, 10:07 AM
  #1  
Senior MemberCaptains Club Member
Thread Starter
 
Join Date: Apr 2001
Location: Texas
Posts: 532
Received 18 Likes on 10 Posts
Default Is it possible to increase speed while decreasing pitch?

2018 2400 Bluewave Purebay. Suzuki 300ap

Boat has a hardtop so a little bit heavier than your average 2400. However, heard several people say it’s a 60 mph boat and I am in the low 50’s.

First prop from dealer was the Suzuki 3x16x23 and only able to get to 5500ish jacked up and trimmed out. Switched to the Suzuki 3x16x 21.5 and can now reach 6,000 wot but only achieving 52 mph with a full tank ( 75) and lightly loaded. Cruises well at 4,200 making 38 mph.

How are these guys getting 60? If I go down more in pitch to touch 6200 or so, won’t my top end suffer?

Any my input on which direction to go would be appreciated.

LW


Last edited by Reel Screamer; 08-08-2018 at 01:03 PM.
Old 08-08-2018, 10:32 AM
  #2  
Admirals Club Admiral's Club Member
 
Join Date: Sep 2004
Location: Mechanicsville VA
Posts: 8,390
Received 926 Likes on 505 Posts
Default

My experience is with a cigarette boat....but the logic is the same: (all testing done the same day within a 2 hour period)

30P Bravo: 52 @ 3,500 and 87 @ 5,700
32P Bravo: 55 @ 3,500 and 83 @ 5,300
28P Maximus: 60 @ 3,500 and 83 @ 5,200 (larger diameter and 5 blade props)

So, yes, you can increase TOP END with a smaller prop if you get the rpms up but cruise speed will suffer.
Likes:
Old 08-08-2018, 10:33 AM
  #3  
Senior Member
 
Join Date: Feb 2014
Location: Melbourne, FL
Posts: 482
Likes: 0
Received 77 Likes on 47 Posts
Default

Are the reports you've heard with or without a hard top? The hard top can kill a good 3-5mph. Were those other boats a single driver and 1/4 tank of fuel? Were they with a current and tail wind? If you're hitting the engine's recommended WOT, then you aren't going to be able to squeeze out more than a couple mph and to me, that's not worth the effort.
Likes:
Old 08-08-2018, 10:51 AM
  #4  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Apr 2001
Location: East Central Florida
Posts: 6,831
Received 1,487 Likes on 746 Posts
Default

Yamaha 300 reports 59.1 MPH @5700 with a "T-TOP". https://yamahaoutboards.com/en-us/ho...2013-04-24_bay
Old 08-08-2018, 11:07 AM
  #5  
Admirals Club Admiral's Club Member
 
Join Date: Aug 2014
Location: Coastal GA
Posts: 1,935
Likes: 0
Received 274 Likes on 164 Posts
Default

The reality is, you are not going to gain the kind of speed you are looking to gain just by changing props. However, the theory behind the answer to your question goes like this:

Assuming all other conditions are the same (weather, weight, trim angle, etc.) and you are trying different props of the same make/model, the pitch that will generate the best top speed is the pitch that puts the engine at its peak horsepower RPM at full speed and WOT. While I cannot be certain, I suspect the peak hp for your engine occurs at 6,000 rpm since the advertised WOT range is 5700 to 6300. Assuming the engine generates exactly 300hp at 6000 rpm, it will generate something less at rpms below and above 6000rpm, which means it cannot overcome as much resistance as it can at 6000rpm.

Don't get me wrong: I'm not saying that propping a boat so that it tops out at the peak HP rpms is always the best approach. I'm just answering your question about pitch changes and maximizing top-end speed.
Likes:
JBS
Old 08-08-2018, 11:25 AM
  #6  
Member
 
Join Date: Aug 2018
Posts: 84
Received 39 Likes on 20 Posts
Default

I don't think the other guys are getting 60. They might have touched it once under ideal conditions, but not regularly. Suzuki barely got 60mph in their own tests.

The T-top is costing you a few miles per hour and so is the full gas tank. That's over 400 pounds of fuel right there.
Likes:
Old 08-08-2018, 11:51 AM
  #7  
Admirals Club Admiral's Club Member
 
Join Date: Aug 2014
Location: Coastal GA
Posts: 1,935
Likes: 0
Received 274 Likes on 164 Posts
Default

No doubt that the drag from the t-top has an impact. The Suzuki test had 30 gals of fuel (280 lbs less weight) but the Yamaha test had a full 75 gals. 7 - 8 mph sure seems like too much of a difference for those factors.
Old 08-08-2018, 11:52 AM
  #8  
Senior Member
 
Join Date: Dec 2014
Location: Land down under
Posts: 14,662
Received 3,340 Likes on 1,993 Posts
Default

Absolutely positively WOT top speed can be obtained while going down in pitch.

There are many many variables in propeller design and construction that affect performance. Materials, diameter, cupping, number of blades, blade geometry (profile/shape), etc.. Anything that can be done to a propeller to increase the efficiency at which it converts horse power to thrust will result in a greater boat speed for a given engine RPM.

Why the focus on WOT top speed only? I almost never run my motor at WOT. Usually can't and most times simply don't want to.
.
Old 08-08-2018, 12:18 PM
  #9  
Senior Member
 
Join Date: Mar 2017
Location: west tn
Posts: 1,120
Received 1,792 Likes on 849 Posts
Default

RS I'd say you are already in the "real world". Forget what you read on the "tests" they are never the real world. Jan 2017 while breaking in my new 2400/300Yam with the original prop (14.25x21M 3 blade Yam) I blipped 62. That was EMPTY other than full fuel and two grown men. NOTHING else, 1 batt, no tackle, no elecs, no troller, no deck seats, nothing. And it was at 400' elevation in upper 30s-40ish cold, dry day. Great conditions for speed honestly. (I've been running 90-100+MPH Allison's for the last 2 decades so these bayboats are slow pigs by comparison but they sure are comfortable to fish from! )

While driving around that day in Jan, as the motors hours would increase I would adjust and "experiment" with what the new boat felt like. I just felt like it wasn't carrying the load and I knew it'd only get MUCH worse after I rigged the boat like I knew I would and began fishing from it. I called my good friend Todd Bucknell of Hydromotive Engineering just outside Cleveland OH. He and his father Thom are amongst the greatest in the custom prop biz, especially the offshore game! He spent some time researching my rig and then produced a prop that he knew would work best for my intended use. Ended up with a 3 blade 15.25x19.

I rigged the boat, 5 batts, 2 onboard chargers, 2 Hbird Mega 10s, 60" 36v Ulterra troller, front/rear deck fishing chairs and being an old bass tournament angler, I carry a "floating BPS" with me whenever I go out. In the west TN July heat and humidity with 5 BIG guys (200# is light!), the 100qt cooler FULL, full fuel, rear seat pad/backrest installed, and rear flip up seats up, 3 of the 5 standing beside me driving and Todd Bucknell riding shotgun the boat ran 54gps and I can't remember exactly now but want to say the tach was right around the 5800 mark? Typically now, 2 man bass/bay fishing load here in west TN or at my place on Okaloosa Island, the boat will run 57-58gps at 6100, cruise 3500 low/mid 30s getting great mileage! I can also lower the trim tabs and if the boat is floating it will take straight off without bow rise and is QUICK! Todd knows how I use a boat and propped it accordingly.

Your T-top is a drag chute, no way around it! You can feel it while towing and the outboard will likewise feel it while running. Nature of the beast and one of their tradeoffs. DON'T believe the BS about the 2400/300 being a 60+mph boat with a full 2-3man fishing LOAD in summer heat. As they say, "I call BS!". It's a full vee hull as well, wont run loaded as fast as some of the pad-vee bay boats out there. But it will outride them in chop because of that full vee in the rear! Back in May 2 buds and I went to Delacroix LA for a few days. We used a guide and he went with us in my BlueWave instead of his personal 24 Skeeter. When we hit Black Bay and the white caps were rolling he paused and worried about the ride. I assured him that was nothing. He admitted he would've had to stand up and used his knees in those conditions with his Skeeter but instead sat up in the passenger seat comfortably as we motored on a few miles out into the bay in my 2400 and fished. (I'm NOT knocking Skeeter, GREAT boats. My first v6 bassboat I ever owned back in the late 80s was a 175 Skeeter. They just utilize a more "pad-vee, bassboat style hull" instead of the pad less, full vee style of the BlueWave. Pad boats typically are faster and draft less. But that same pad yields a little bit bumpier ride, just a style difference, not a quality difference.)

Prop your boat/s for "max load, summer time conditions" not the best/fastest prop under lighter, cooler, "perfect" conditions. Lugging a motor is never good for it. I'd rather turn it 500Rs more than recommended than 500Rs under! But with a prop test or two you can find that proverbial "sweet spot" and honestly "that spot" is a constant change, load, conditions, power etc... nothing is in concrete or lasts forever. You just gotta get as close as possible and realize there's no 100% perfect for all situations prop. (LOL us guys that run truly fast boats typically have a wall FULL of props. This owning only 1-2 props per boat is new to me. )

Last edited by HatchieLuvr; 08-08-2018 at 12:24 PM.
Likes:
Old 08-08-2018, 12:31 PM
  #10  
Admirals Club Admiral's Club Member
 
Join Date: Aug 2005
Location: Jupiter, Florida
Posts: 5,881
Likes: 0
Received 191 Likes on 136 Posts
Default

Smaller pitch with more rpm and less slip will be faster.
Old 08-08-2018, 12:52 PM
  #11  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Apr 2001
Location: East Central Florida
Posts: 6,831
Received 1,487 Likes on 746 Posts
Default

Not to derail this thread or anything, but for HatchieLuvr, I was wondering if anyone has put a Verado 400R on an Allison/Bullet style bass boat and if so, what was the top end? Thanks.
Old 08-08-2018, 01:09 PM
  #12  
Senior MemberCaptains Club Member
Thread Starter
 
Join Date: Apr 2001
Location: Texas
Posts: 532
Received 18 Likes on 10 Posts
Default

All great points to consider. Thanks THT. Keep them coming.
Old 08-08-2018, 03:42 PM
  #13  
Senior Member
 
Join Date: Aug 2016
Location: Plantation, FL
Posts: 192
Received 54 Likes on 46 Posts
Default

Originally Posted by Ric232 View Post
The reality is, you are not going to gain the kind of speed you are looking to gain just by changing props. However, the theory behind the answer to your question goes like this:

Assuming all other conditions are the same (weather, weight, trim angle, etc.) and you are trying different props of the same make/model, the pitch that will generate the best top speed is the pitch that puts the engine at its peak horsepower RPM at full speed and WOT. While I cannot be certain, I suspect the peak hp for your engine occurs at 6,000 rpm since the advertised WOT range is 5700 to 6300. Assuming the engine generates exactly 300hp at 6000 rpm, it will generate something less at rpms below and above 6000rpm, which means it cannot overcome as much resistance as it can at 6000rpm.

Don't get me wrong: I'm not saying that propping a boat so that it tops out at the peak HP rpms is always the best approach. I'm just answering your question about pitch changes and maximizing top-end speed.
This. Your max hp may be at redline, should be able to find that somewhere on the interweb, but decreasing pitch to let the motor turn faster can make the entire rig faster.
Old 08-08-2018, 05:57 PM
  #14  
Senior Member
 
Join Date: Mar 2017
Location: west tn
Posts: 1,120
Received 1,792 Likes on 849 Posts
Default

Originally Posted by Onewolf View Post
Not to derail this thread or anything, but for HatchieLuvr, I was wondering if anyone has put a Verado 400R on an Allison/Bullet style bass boat and if so, what was the top end? Thanks.
Sent you a PM!
Old 08-08-2018, 06:03 PM
  #15  
Admirals Club Admiral's Club Member
 
Join Date: May 2011
Location: Louisiana and Morehead City N.C.
Posts: 12,512
Received 1,322 Likes on 939 Posts
Default

Originally Posted by Onewolf View Post
Yamaha 300 reports 59.1 MPH @5700 with a "T-TOP". https://yamahaoutboards.com/en-us/ho...2013-04-24_bay
Yea that's more like the numbers he should see.

My SH 24 which was heavier, bigger hardtop, much bigger console, higher freeboard and slower hull hit 55 with full fuel and light load.

His boat should be 58 no problems.
Old 08-08-2018, 06:11 PM
  #16  
Senior MemberCaptains Club Member
Thread Starter
 
Join Date: Apr 2001
Location: Texas
Posts: 532
Received 18 Likes on 10 Posts
Default

Originally Posted by captain28570 View Post
Yea that's more like the numbers he should see.

My SH 24 which was heavier, bigger hardtop, much bigger console, higher freeboard and slower hull hit 55 with full fuel and light load.

His boat should be 58 no problems.

i am am thinking the same thing. Talked to another guy at the dock yesterday with the same boat. He had an aluminum top vs my hard top but he was seeing 62. Maybe these Suzuki props are just junk.
Old 08-08-2018, 06:16 PM
  #17  
Senior MemberCaptains Club Member
Thread Starter
 
Join Date: Apr 2001
Location: Texas
Posts: 532
Received 18 Likes on 10 Posts
Default

Originally Posted by HatchieLuvr View Post
RS I'd say you are already in the "real world". Forget what you read on the "tests" they are never the real world. Jan 2017 while breaking in my new 2400/300Yam with the original prop (14.25x21M 3 blade Yam) I blipped 62. That was EMPTY other than full fuel and two grown men. NOTHING else, 1 batt, no tackle, no elecs, no troller, no deck seats, nothing. And it was at 400' elevation in upper 30s-40ish cold, dry day. Great conditions for speed honestly. (I've been running 90-100+MPH Allison's for the last 2 decades so these bayboats are slow pigs by comparison but they sure are comfortable to fish from! )

While driving around that day in Jan, as the motors hours would increase I would adjust and "experiment" with what the new boat felt like. I just felt like it wasn't carrying the load and I knew it'd only get MUCH worse after I rigged the boat like I knew I would and began fishing from it. I called my good friend Todd Bucknell of Hydromotive Engineering just outside Cleveland OH. He and his father Thom are amongst the greatest in the custom prop biz, especially the offshore game! He spent some time researching my rig and then produced a prop that he knew would work best for my intended use. Ended up with a 3 blade 15.25x19.

I rigged the boat, 5 batts, 2 onboard chargers, 2 Hbird Mega 10s, 60" 36v Ulterra troller, front/rear deck fishing chairs and being an old bass tournament angler, I carry a "floating BPS" with me whenever I go out. In the west TN July heat and humidity with 5 BIG guys (200# is light!), the 100qt cooler FULL, full fuel, rear seat pad/backrest installed, and rear flip up seats up, 3 of the 5 standing beside me driving and Todd Bucknell riding shotgun the boat ran 54gps and I can't remember exactly now but want to say the tach was right around the 5800 mark? Typically now, 2 man bass/bay fishing load here in west TN or at my place on Okaloosa Island, the boat will run 57-58gps at 6100, cruise 3500 low/mid 30s getting great mileage! I can also lower the trim tabs and if the boat is floating it will take straight off without bow rise and is QUICK! Todd knows how I use a boat and propped it accordingly.

Your T-top is a drag chute, no way around it! You can feel it while towing and the outboard will likewise feel it while running. Nature of the beast and one of their tradeoffs. DON'T believe the BS about the 2400/300 being a 60+mph boat with a full 2-3man fishing LOAD in summer heat. As they say, "I call BS!". It's a full vee hull as well, wont run loaded as fast as some of the pad-vee bay boats out there. But it will outride them in chop because of that full vee in the rear! Back in May 2 buds and I went to Delacroix LA for a few days. We used a guide and he went with us in my BlueWave instead of his personal 24 Skeeter. When we hit Black Bay and the white caps were rolling he paused and worried about the ride. I assured him that was nothing. He admitted he would've had to stand up and used his knees in those conditions with his Skeeter but instead sat up in the passenger seat comfortably as we motored on a few miles out into the bay in my 2400 and fished. (I'm NOT knocking Skeeter, GREAT boats. My first v6 bassboat I ever owned back in the late 80s was a 175 Skeeter. They just utilize a more "pad-vee, bassboat style hull" instead of the pad less, full vee style of the BlueWave. Pad boats typically are faster and draft less. But that same pad yields a little bit bumpier ride, just a style difference, not a quality difference.)

Prop your boat/s for "max load, summer time conditions" not the best/fastest prop under lighter, cooler, "perfect" conditions. Lugging a motor is never good for it. I'd rather turn it 500Rs more than recommended than 500Rs under! But with a prop test or two you can find that proverbial "sweet spot" and honestly "that spot" is a constant change, load, conditions, power etc... nothing is in concrete or lasts forever. You just gotta get as close as possible and realize there's no 100% perfect for all situations prop. (LOL us guys that run truly fast boats typically have a wall FULL of props. This owning only 1-2 props per boat is new to me. )

Thanks for that write up. I will do some experimenting. Do you have a suggestion on what I should go with? Amazing to me that the dealer started me out with a 23 pitch. It wasn’t anywhere close.
Old 08-08-2018, 06:22 PM
  #18  
Senior Member
 
Join Date: Jul 2013
Posts: 1,439
Received 197 Likes on 102 Posts
Default

Originally Posted by Reel Screamer View Post



i am am thinking the same thing. Talked to another guy at the dock yesterday with the same boat. He had an aluminum top vs my hard top but he was seeing 62. Maybe these Suzuki props are just junk.
What are they made of?
Old 08-08-2018, 07:09 PM
  #19  
Senior Member
 
Join Date: Apr 2006
Posts: 6,244
Received 1,427 Likes on 885 Posts
Default

Have you done the prop slip calc for your current prop & setup? Couple of minutes on the calculator and you should have a decent idea about how that prop is performing. Reducing slip by changing prop diameter or design and make a big difference is you have a lot of slip with the current prop.
Rough figures - your current 16x21.5 running 52mph @ 6000rpm (is that all correct?) is running a bit over 10%. If you could reduce that to say a really good number like 4% (might be tough) then you get 56mph with the current pitch. That might involve a little cupping or a little more diameter/blade area etc as some prop expert may be able to advise. To crack 60mph you would need to be running a 23" pitch prop at 4% slip @ 6000rpm. That sounds like it might be an unrealistic goal unless you can get some extra hp or reduce drag. Just getting a better 21.5"prop that has less slip might get you to 55 or 56mph, but unless you can turn a good 23" pitch prop to 6000rpm I don't see 60mph happening with your current loading. would be interesting if you could borrow a 15.5x23 or 15.75x23 3 blade prop to see what they would do (i.e. more rpms but carry the bigger pitch). Trouble is that there is a chance that your slip numbers might get worse with the smaller diameter and you could go backwards. Hence I would only try that with a loaner prop.
Likes:
Old 08-08-2018, 08:29 PM
  #20  
Senior Member
 
Join Date: Feb 2013
Posts: 1,447
Received 313 Likes on 194 Posts
Default

Originally Posted by Ric232 View Post
... pitch that puts the engine at its peak horsepower RPM at full speed and WOT. ...
Most engines produce maximum horsepower at less than max rpm or WOT. Once you get above a certain rpm the engine efficiency starts to decrease for a number of reasons.

For example:

Likes:

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.