28 heat prop issues
06-04-2011, 10:59 PM
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28 heat prop issues
Hi i Have a 1995 28 heat with a bullet engines 625 hp 540 having problems finding the right prop I would appreciate some help
Here is where my problem lies most of your prop testing forum topics are on step hull heats.
Here are some of the props i have tried.26 bravo 1 reved 5250 73 mph gps.26 bravo 1 labbed .70 cup 5350 74mph the boat needs way too much trim to get these speeds and porpoises bad at over 70 I trim down to get rid of it and the speed drops off.I also tried a 25 mirage plus no porpoising but speed fell to 71.5 at 5200.I also tried a 28 bravo 1 went 67mph at 4700.Please if you have any experience with the non stepped heat I would appreciate it I would like to get a few more miles per hour out of it thanks
Ps the engine makes power at 5400. bravo 1 xr 1.5
Here is where my problem lies most of your prop testing forum topics are on step hull heats.
Here are some of the props i have tried.26 bravo 1 reved 5250 73 mph gps.26 bravo 1 labbed .70 cup 5350 74mph the boat needs way too much trim to get these speeds and porpoises bad at over 70 I trim down to get rid of it and the speed drops off.I also tried a 25 mirage plus no porpoising but speed fell to 71.5 at 5200.I also tried a 28 bravo 1 went 67mph at 4700.Please if you have any experience with the non stepped heat I would appreciate it I would like to get a few more miles per hour out of it thanks
Ps the engine makes power at 5400. bravo 1 xr 1.5
06-05-2011, 08:45 AM
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Welcome to the Nordic Forum Villain,
I have helped my friend Butch Fletcher with his '96 Heat, pad vee hull. There are several other pad vees in town.
I noticed:
The older boats seem to be layed up much lighter (or at least his is).
They have a relatively deep X-dimension (specifically the vertical distance from the driveshaft to the bottom of the boat). That's where your problems are coming from. With this deeper X-dimension, they acellerate well, and have normally have plenty of lift (sometimes too much with newer design, larger diameter props). With stock motors, in the 400/425HP range, this worked OK.
He was running a 14.75" diameter X 27" Spinelli four blade with his stock XD. We put a -2" IMCO short lower on the boat, and switched to a labbed Bravo 1 four blade 15.25" X 26", and it handles better. Still planes off great, less porpoising, no chinewalk at speed/wot.
The props you are testing are designed to run near the surface (called semi-surfacing), and that's why they work better when you over trim, but that's also why your boat porpoises, from excessive trim. Over trimming can also cause frictional horsepower losses, excessive drive train wear (U-joint, gimble bearings), and handling issues like chine walking.
If you can get your hands on a short IMCO lower (probably a -2") to test, I think your porpoising problems will go away, your boat will be faster and work better all around.
With your standard depth XR lower, you'll have better luck by running a smaller diameter prop, like 14.75" to 15", in the 26/27" pitch range, because it's running completely submerged.
If you have a good propeller shop to work with, they can reduce the diameter for you by grinding the blade tips down. They can also adjust the cup to add or reduce lift as needed.
That will reduce your porpoising, and raise your RPMs.
You've got a good engine/hull combination. As the horsepower and speed go up, it's normal to run into some rigging/handling/proping quirks. It's similar to sticking your 540/625 into a car with a stock suspension. It probably wouldn't handle properly (without some suspension upgrades) either.
Good luck and keep us posted.
Regards,
Steve
I have helped my friend Butch Fletcher with his '96 Heat, pad vee hull. There are several other pad vees in town.
I noticed:
The older boats seem to be layed up much lighter (or at least his is).
They have a relatively deep X-dimension (specifically the vertical distance from the driveshaft to the bottom of the boat). That's where your problems are coming from. With this deeper X-dimension, they acellerate well, and have normally have plenty of lift (sometimes too much with newer design, larger diameter props). With stock motors, in the 400/425HP range, this worked OK.
He was running a 14.75" diameter X 27" Spinelli four blade with his stock XD. We put a -2" IMCO short lower on the boat, and switched to a labbed Bravo 1 four blade 15.25" X 26", and it handles better. Still planes off great, less porpoising, no chinewalk at speed/wot.
The props you are testing are designed to run near the surface (called semi-surfacing), and that's why they work better when you over trim, but that's also why your boat porpoises, from excessive trim. Over trimming can also cause frictional horsepower losses, excessive drive train wear (U-joint, gimble bearings), and handling issues like chine walking.
If you can get your hands on a short IMCO lower (probably a -2") to test, I think your porpoising problems will go away, your boat will be faster and work better all around.
With your standard depth XR lower, you'll have better luck by running a smaller diameter prop, like 14.75" to 15", in the 26/27" pitch range, because it's running completely submerged.
If you have a good propeller shop to work with, they can reduce the diameter for you by grinding the blade tips down. They can also adjust the cup to add or reduce lift as needed.
That will reduce your porpoising, and raise your RPMs.
You've got a good engine/hull combination. As the horsepower and speed go up, it's normal to run into some rigging/handling/proping quirks. It's similar to sticking your 540/625 into a car with a stock suspension. It probably wouldn't handle properly (without some suspension upgrades) either.
Good luck and keep us posted.
Regards,
Steve
Last edited by Steve Zuckerman; 06-05-2011 at 03:00 PM.
06-05-2011, 11:00 AM
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Wow Thanks for the heat lessons. I appreciate the help I was already measuring the drive height yesterday compared to my buddies powerquest and was amazed there was quite a few inches difference.
I hate to bug you again but I now have a few more questions.Going with the smaller diameter prop is obviously the cheaper alternative.Is there a large difference between in mph between the small diameter prop set properly for my x dim and going with the shorty drive and a big diam prop. I guess what i am trying to say is that if there is going to be like a 3 plus mph difference I would probably like to go with the shorty. I would really like quite a few more mph Thanks for all the help.
I hate to bug you again but I now have a few more questions.Going with the smaller diameter prop is obviously the cheaper alternative.Is there a large difference between in mph between the small diameter prop set properly for my x dim and going with the shorty drive and a big diam prop. I guess what i am trying to say is that if there is going to be like a 3 plus mph difference I would probably like to go with the shorty. I would really like quite a few more mph Thanks for all the help.
06-05-2011, 11:38 AM
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Glad to be of help. We can use my buddy's boat as guide for the pad vee hulls. His is one year model newer so they should be simiar in weight and performance.
He has 4.25" stroker 454 with 496 cu. ins. It is also supercharged with a B&M 250 and 2 four 770CFM carbs. We've never dynoed his motor, but it should be making 675/700HP. His boat runs in the low 80s. That's with the Imco -2 and a labbed 15.25" x 26" Bravo 1 four blade.
The small diameter prop was to me, a bandaid for a deep X dimension with a fair amount of horsepower, but it did work. He did have to overtrim to get the boat to perform, and just like yours, it porpoised a lot.
Any boat, pad vee, step vee, tunnel, tunnel vee, will be the most efficient if you can get it to lift properly with the propshaft parallel to the hull. That way, you are using whatever horsepower you have available to push your boat, not to lift it. The higher the horsepower to weight ratio is, the higher the X dimension you can run. If you think about running the small prop, trimmed way out, it is running "in a bind" and not very efficient.
The best you'll get with your current setup and the perfect prop for that setup will still be a compromise vs an IMCO -2" and a blueprinted Bravo or Hydromotive 4 blade. When you run a higher XD, you'll need less trim to semisurface a larger diameter and possible higher pitch propeller. Possibly a 5 mph differential. The other advantage to a higher XD is where all this started, less lower unit or drive drag. You've probably see high performace outboards with jack plates used to raise the motor into surfacing or semisurfacing transom height (or XD). You may have seen step vees and race/poker run tunnels with race drives at or above the bottom of the boat. All this is designed to get rid of lower unit parasitic drag, and run larger diameter, higher pitch propellers. It does work, very well.
PS I see IMCO shortys for sale in the drive section regularly.
Just make sure you are getting one with high grade internals.
FYI, we do know 600/625 HP will get 80 mph on the step hulls. Some of it is the hull and some of it is the much higher XD the factory used on these boats.
Regards,
Steve
He has 4.25" stroker 454 with 496 cu. ins. It is also supercharged with a B&M 250 and 2 four 770CFM carbs. We've never dynoed his motor, but it should be making 675/700HP. His boat runs in the low 80s. That's with the Imco -2 and a labbed 15.25" x 26" Bravo 1 four blade.
The small diameter prop was to me, a bandaid for a deep X dimension with a fair amount of horsepower, but it did work. He did have to overtrim to get the boat to perform, and just like yours, it porpoised a lot.
Any boat, pad vee, step vee, tunnel, tunnel vee, will be the most efficient if you can get it to lift properly with the propshaft parallel to the hull. That way, you are using whatever horsepower you have available to push your boat, not to lift it. The higher the horsepower to weight ratio is, the higher the X dimension you can run. If you think about running the small prop, trimmed way out, it is running "in a bind" and not very efficient.
The best you'll get with your current setup and the perfect prop for that setup will still be a compromise vs an IMCO -2" and a blueprinted Bravo or Hydromotive 4 blade. When you run a higher XD, you'll need less trim to semisurface a larger diameter and possible higher pitch propeller. Possibly a 5 mph differential. The other advantage to a higher XD is where all this started, less lower unit or drive drag. You've probably see high performace outboards with jack plates used to raise the motor into surfacing or semisurfacing transom height (or XD). You may have seen step vees and race/poker run tunnels with race drives at or above the bottom of the boat. All this is designed to get rid of lower unit parasitic drag, and run larger diameter, higher pitch propellers. It does work, very well.
PS I see IMCO shortys for sale in the drive section regularly.
Just make sure you are getting one with high grade internals.
FYI, we do know 600/625 HP will get 80 mph on the step hulls. Some of it is the hull and some of it is the much higher XD the factory used on these boats.
Regards,
Steve
Last edited by Steve Zuckerman; 06-05-2011 at 03:03 PM.
06-05-2011, 12:05 PM
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06-05-2011, 06:33 PM
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I would love to chat a little more if I could have your email I would email u pics of the boat and stuff.I would love to see pics of yours
Ps I am already pricing out drives.Thanks.
Ps I am already pricing out drives.Thanks.
06-07-2011, 06:47 PM
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Hi Villian,
Since you're new to the site, I thought I would tell you that you can send PMs and email to other members by clicking on their names. Then you'll have a menu to choose from.
BTW, here are a couple of pictures of the "business end" of my boat. Most of the 2001+ step hull owners have the opposite issue of the earlier boats. Our XDs are very high. Mine is 19.25"s, so I have a 1" spacer on my standard length IMCO lower to lower it to an effective 18.25"s. If you look at the drive height in the pic on the right, you'll notice it is much higher than yours. FYI, I also changed out the factory Bennett tabs. They are mounted too close to the hull centerline (IMO). I mounted the Eddie's out at the chines. They control chinewalk and listing much better there.
I need to get you some pics of Butch's '96 with the IMCO -2" lower on it, since that's what you are working on. Send your JPEGs to me or post them on here. Some of the other pad vee owners may some ideas for you too.
Regards,
Steve
Since you're new to the site, I thought I would tell you that you can send PMs and email to other members by clicking on their names. Then you'll have a menu to choose from.
BTW, here are a couple of pictures of the "business end" of my boat. Most of the 2001+ step hull owners have the opposite issue of the earlier boats. Our XDs are very high. Mine is 19.25"s, so I have a 1" spacer on my standard length IMCO lower to lower it to an effective 18.25"s. If you look at the drive height in the pic on the right, you'll notice it is much higher than yours. FYI, I also changed out the factory Bennett tabs. They are mounted too close to the hull centerline (IMO). I mounted the Eddie's out at the chines. They control chinewalk and listing much better there.
I need to get you some pics of Butch's '96 with the IMCO -2" lower on it, since that's what you are working on. Send your JPEGs to me or post them on here. Some of the other pad vee owners may some ideas for you too.
Regards,
Steve
Last edited by Steve Zuckerman; 06-07-2011 at 06:58 PM.
06-11-2011, 08:23 AM
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It's a cell phone pic, but I think you'll see how the -2 IMCO raises the propshaft depth on the lower XD boats.
This Butch's '96 Heat.
BTW, keep a close eye on your water pressure with the IMCO lower. It rams water into a nose pickup and can send your pressure through the roof. You may need to add some water pressure relief(s) to lower it. Merc makes a nice one that opens @ 30PSI. You'll see a through hull fitting in this pic that comes through the swin platform. We've mounted our dumps there to spray water on the the top of the drive for a little extra cooling.
Regards,
Steve
This Butch's '96 Heat.
BTW, keep a close eye on your water pressure with the IMCO lower. It rams water into a nose pickup and can send your pressure through the roof. You may need to add some water pressure relief(s) to lower it. Merc makes a nice one that opens @ 30PSI. You'll see a through hull fitting in this pic that comes through the swin platform. We've mounted our dumps there to spray water on the the top of the drive for a little extra cooling.
Regards,
Steve
Last edited by Steve Zuckerman; 06-11-2011 at 09:03 AM.
06-13-2011, 09:11 AM
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I went out and bought a merc sportmaster shorty lower this weekend.
I had water pressure issues before with the standard xr I plugged off the nose pickups and my pressure went down to normal.I have a few options to try I dont want to get as high as 30 so I might drill the thermostat out, or i have water flow restrictors as well and plug the bypass hose off.I will test this week and let you know thanks again.
I had water pressure issues before with the standard xr I plugged off the nose pickups and my pressure went down to normal.I have a few options to try I dont want to get as high as 30 so I might drill the thermostat out, or i have water flow restrictors as well and plug the bypass hose off.I will test this week and let you know thanks again.
