Porpoising not on purpose

CABINDOC · 05-04-10, 08:44 PM

I have a porpoising problem and was wondering if anyone out there has any insight.
The problem: Porpoising before getting to the sweet spot while trimming @ speed.
The boat: 93 Hydra-Sports 170 fs. 17’ fish/sk.
The motor: Johnson 90 2 stroke runs well as far as I can tell based on my observations, WOT and speed
The prop: I have tried 3 and 4 blade, right now; prop is good based on speed/RPM @ WOT and the way it gets up on plane.

The load. I have tried it alone and with max capacity. I have tried shifting all the people forward of the wind screen to see if I could get there before the porpoise showed up, no luck. Has room for 2 trolling motor batteries in the rear bilge, I don’t have them in right now. Tank is ½ full and I have been running with the live well empty.

Is this a design flaw with these boats? I have only had it for 2 years and it has always done it.

CABINDOC · 05-06-10, 07:55 AM

UPDATE

It appears as though the cav plate is 4-6 inches above the bottom of tho boat. Could this be why I'm having a problem?

MississippiBoy · 05-06-10, 08:53 AM

Could be...I'm no boat expert by any means, and I didn't even stay at a Holiday Inn Express last night, but there's a couple of guys on here that have been playing with boats for years. One of them should be able to help you out, with a little more info.
You'll need an accurate measurement of the distance from prop to pad. In other words, how far the center of the prop is below the bottom of the boat. Here's a link on how to do this properly: http://www.bassboatcentral.com/measuring.htm #2 is the one I'm referring to.
That measurement should give some of the boat gurus an idea about what might help you. Good luck.

Abbeysdad · 05-06-10, 01:16 PM

(just thinkin out loud....)

Photos of trim down and trim 'sweet' spot, on the trailer may also reveal an alignment issue that could cause the fish action.

carolina-rig-01 · 05-06-10, 07:54 PM

Quote:

Originally Posted by Abbeysdad

(just thinkin out loud....)

Photos of trim down and trim 'sweet' spot, on the trailer may also reveal an alignment issue that could cause the fish action.

If I understand what he means by sweet spot it isn't something that you would be able to replicate on the trailer because the only way to know when you are there is by feel and performance when running down the lake.

Abbeysdad · 05-06-10, 08:05 PM

Quote:

Originally Posted by carolina-rig-01

If I understand what he means by sweet spot it isn't something that you would be able to replicate on the trailer because the only way to know when you are there is by feel and performance when running down the lake.

Well, not with my boat - I had to find it initially, but I have a gauge and know exactly where the sweet spot is. But yer right, w/o a gauge it would just be 'by guess or by gosh' on the trailer.

carolina-rig-01 · 05-06-10, 08:41 PM

Quote:

Originally Posted by Abbeysdad

Well, not with my boat - I had to find it initially, but I have a gauge and know exactly where the sweet spot is. But yer right, w/o a gauge it would just be 'by guess or by gosh' on the trailer.

Whatever dude, guess I have no clue what I am talking about despite several years of running bass boats. Glad you were so lucky to gain such a vast amount of excellence with bass boat setups in your short time as a boat owner.

P.S. Every boat I have owned has had a trim guage and not one of them had a sweet spot marked on the guage. It's all about seat time.

CABINDOC · 05-06-10, 09:53 PM

First, thanx all for your inpuit. I finaly feel as though I'm making progress on this problem.

I do have a gauge and I know where about the gauge was right before it starts to porpoise. I'll take pics tommorrow in that position and all the way down and measure it as mississippiboy sugests......Stay tuned......

Remember, I cannot get it to that sweet spot due to the porpoising.

Rebbasser · 05-06-10, 10:35 PM

Doc, it has been my experience that porpoising is a matter of both speed and trim. Mine will porpoise when I throttle back from WOT and don't trim it down. I'm guessing the sweet spot you are referring to is at WOT. I don't know there is one set spot on the trim for it. I think you have to find it every time out because every trip is probably a little different-a different partner that weighs more/less, different gear, etc. can change the weight of the boat so there may be a little variation in where the sweet spot is depending on the conditions.

CABINDOC · 05-06-10, 11:11 PM

Quote:

Originally Posted by Rebbasser

Doc, it has been my experience that porpoising is a matter of both speed and trim. Mine will porpoise when I throttle back from WOT and don't trim it down. I'm guessing the sweet spot you are referring to is at WOT. I don't know there is one set spot on the trim for it. I think you have to find it every time out because every trip is probably a little different-a different partner that weighs more/less, different gear, etc. can change the weight of the boat so there may be a little variation in where the sweet spot is depending on the conditions.

Yes, your right. However, I know from other boats where the boat should be riding on the hull and this one seems to be breaking the waterline amidship rather than back further closer to the transom. This is the case no mater what the weight. I also own a 19' bayliner i/o and that boat never porpoises. If I over trim it, the prop breaks and cavitates. It's just not right.....

carolina-rig-01 · 05-06-10, 11:25 PM

It sounds to me like it is a motor height problem. Off the top of my head it sounds as if your motor is too low but the best thing to do is get the measurements and go from there.

CABINDOC · 05-06-10, 11:33 PM

Quote:

Originally Posted by carolina-rig-01

It sounds to me like it is a motor height problem. Off the top of my head it sounds as if your motor is too low but the best thing to do is get the measurements and go from there.

Yep, first thim tommorrow, but I actually think the prop sits too high...

Once I have the measurement, I'll post here and then I'm going to try to reach out to Hydra- Sports, even though they have been bought out, to see what the spec calls for on this model.

Captmikestarrett · 05-07-10, 08:56 AM

The top of the lower unit has a plate. That plate should be at waterline when running. Above it, it will porpoise. To far below it and it will porpoise on trim out.

I had a Gambler with hydrulic lift plate and played with it up and down to figure out why it acted like it did.

Capt Mike

Abbeysdad · 05-07-10, 01:48 PM

Quote:

Originally Posted by carolina-rig-01

Whatever dude, guess I have no clue what I am talking about despite several years of running bass boats. Glad you were so lucky to gain such a vast amount of excellence with bass boat setups in your short time as a boat owner.

P.S. Every boat I have owned has had a trim guage and not one of them had a sweet spot marked on the guage. It's all about seat time.

I'm just saying I can trim up to the the exact same place on my trim gauge for the sweet spot (a bit lower than the picture here), just like I can say this boat will plane at about 4000rpm, about 25mph. I've played with it many times and end up at the same place for the sweet spot. I guess I don't understand why that sounds unbelievable. And yes, I may only have 120 hours with this boat on the water, but it ain't a space shuttle either.

CABINDOC · 05-07-10, 07:58 PM

Okay, I measured the distance of the center of the wheel to the bottom of the boat and the wheel is 5 3/4" below the bottom. When on plane, I can see the top of the hydrafoils. Also, the pitch on the prop is a 17. I could not replicate the position of the outboard when I was close to the best position. Also, someone earlier mention WOT. I usually dont run WOT, this occours at any speed, but I usually run @ 4,200 rpm and with this prop, thats puts me at about 28mph.

Bender · 05-07-10, 10:11 PM

That sounds a bit too low, but I do not know that hull. Most average bassboats that I have messed with are somewhere between 2 1/2" to 3 1/2" below pad. Do you have a water pressure gauge? I realize without a jackplate you don't want to move it around a whole bunch to find out where it should be but I would take it up and watch the water pressure gauge, you don't want that to get low.

I just looked through the Hydrasport Owner's List on BBC and the closest I can find to your boat is a guy running one at 4" below pad and his only bounces from 45-50. He had a fin on and that made it worse.

CABINDOC · 05-07-10, 10:35 PM

Quote:

Originally Posted by Bender

That sounds a bit too low, but I do not know that hull. Most average bassboats that I have messed with are somewhere between 2 1/2" to 3 1/2" below pad. Do you have a water pressure gauge? I realize without a jackplate you don't want to move it around a whole bunch to find out where it should be but I would take it up and watch the water pressure gauge, you don't want that to get low.

I just looked through the Hydrasport Owner's List on BBC and the closest I can find to your boat is a guy running one at 4" below pad and his only bounces from 45-50. He had a fin on and that made it worse.

Interesting.... If you find a tech manual on this boat, I w/b interested.

CABINDOC · 05-09-10, 03:16 PM

Update

This motor is a long shaft, 20"
I measure the transom @ 22" to the bottom of the boat
I'm wondering if I w/b better off with a xtra long shaft 25"?

lilmule · 05-09-10, 04:46 PM

No your to deep now,propshaft about 3-3 1/2 under the pad with a stock gear case,porpoise is caused by excessive trim that low.
Raising it the motor it will take less trim.Odds are with the motor at a less trim position running level it wont do it now even.
And any motor should be run in the power band to insure long life,not exactly wot but in the band 4 to 4200 seems a tad low.
When trimmed right the rooster tail behind the boat is no more than motor high,often less .

CABINDOC · 05-09-10, 08:02 PM

Quote:

Originally Posted by lilmule

No your to deep now,propshaft about 3-3 1/2 under the pad with a stock gear case,porpoise is caused by excessive trim that low.
Raising it the motor it will take less trim.Odds are with the motor at a less trim position running level it wont do it now even.
And any motor should be run in the power band to insure long life,not exactly wot but in the band 4 to 4200 seems a tad low.
When trimmed right the rooster tail behind the boat is no more than motor high,often less .

I dont get it. Everything I read and even my mechanic says that the cav plate s/b even with the pad. Even in the manual, it shows that. My transon to pad measures 22" Also, my prop is 5 3/4" below pad. Most people, your self included, say the prop s/b 2-4" below pad. Cav plate too high, prop too low...I dont get it...Wrong foot on motor?

1FASTLASER · 05-17-10, 06:15 AM

Ole carolina gets the cookie on the sweet spot.....the sweet spot will vary depending on load etc etc and will be close but not the same every time out. TAKES ALOT of seat time to figure it out.

Second you need to get the prop shaft measurements and start there and as well take a look at the prop. Is the prop in good shape ???? You also need to realize that boat is underpowered. 90 hp on a 17ft boat is bare minimum. Porpising can be caused from a boat "trying to lift" but not having enough hp to sustain the lift.........most generally this is the cause.

CABINDOC · 05-17-10, 09:31 AM

Thanks for your input. to answer your questions; the prop sits about 5 1/2 below pad, the cav plate sits about 2" above pad, the prop is near new, no dings or dents. The prop is a Solas 13.25x17p and I also have a 4 blade 15p I use for pulling skiers and it does it as well. This boat max's out @ 32mph with WOT @ about 5,000.

I hear what your saying about the 90, but I have had some corespondance with others with similar hulls and motor combinations and they dont report the problem and they report higher speeds. also, I had a Center console with a 90 on it, it was a heavy boat, double hull with flotation, and I had no porpoising and a top speed of 40mph.

How does on test the output performance of an outboard on a bench? Is there a dyno for motors?

So, although I agree it is on the lower end of power compared to most bass boats, I also think it should be doing better than this.

lilmule · 05-17-10, 10:09 AM

Simple solution raise the motor,a lil at a time,it should disappear,raising no higher than needed to go away it wont hurt the hole shot for pulling skiers
With a 2-1 gear ratio,5000 rpm 17 P prop,slip ten percent speed should be right at 37mph.
Check with those others getting more speed they arnt 5 1/2 under the pad,I bet.
Its easier if on a jack plate if not go up one hole on the motor mounting.

GregK9 · 05-17-10, 12:13 PM

Quote:

Originally Posted by 1FASTLASER

boat is underpowered. 90 hp on a 17ft boat is bare minimum. Porpising can be caused from a boat "trying to lift" but not having enough hp to sustain the lift.........most generally this is the cause.

I have a 70HP on a 17 1/2 foot boat - wayyy underpowered!

Nonetheless, when it's starts porpising I just trim down a bit and it stops.

I also have one of these:

http://www.cabelas.com/cabelas/en/te...box.jsp.form23

it helped with the porpising a little bit but made a HUGE difference with my hole shot!!

CABINDOC · 05-17-10, 08:54 PM

Thanx both for your input. I agree and am going to try both. First the Hydrafoil, then the lift.

05-04-10, 08:44 PM	#1
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Porpoising not on purpose I have a porpoising problem and was wondering if anyone out there has any insight. The problem: Porpoising before getting to the sweet spot while trimming @ speed. The boat: 93 Hydra-Sports 170 fs. 17’ fish/sk. The motor: Johnson 90 2 stroke runs well as far as I can tell based on my observations, WOT and speed The prop: I have tried 3 and 4 blade, right now; prop is good based on speed/RPM @ WOT and the way it gets up on plane. The load. I have tried it alone and with max capacity. I have tried shifting all the people forward of the wind screen to see if I could get there before the porpoise showed up, no luck. Has room for 2 trolling motor batteries in the rear bilge, I don’t have them in right now. Tank is ½ full and I have been running with the live well empty. Is this a design flaw with these boats? I have only had it for 2 years and it has always done it.

05-06-10, 08:53 AM	#3
MississippiBoy BassFishin.Com Super Veteran Join Date: May 2007 Location: Ridgeland MS Posts: 3,923	Could be...I'm no boat expert by any means, and I didn't even stay at a Holiday Inn Express last night, but there's a couple of guys on here that have been playing with boats for years. One of them should be able to help you out, with a little more info. You'll need an accurate measurement of the distance from prop to pad. In other words, how far the center of the prop is below the bottom of the boat. Here's a link on how to do this properly: http://www.bassboatcentral.com/measuring.htm #2 is the one I'm referring to. That measurement should give some of the boat gurus an idea about what might help you. Good luck. __________________ I smell smoke, and I hear sirens. Do you think that's a problem?

05-06-10, 01:16 PM	#4
Abbeysdad BassFishin.Com Super Veteran Join Date: Jul 2008 Location: Central NY - Finger Lakes Posts: 1,307	(just thinkin out loud....) Photos of trim down and trim 'sweet' spot, on the trailer may also reveal an alignment issue that could cause the fish action. __________________ Fish now, work later

05-06-10, 10:35 PM	#9
Rebbasser BassFishin.Com Premier Elite Join Date: Jun 2003 Location: San Antonio, TX Posts: 10,141	Doc, it has been my experience that porpoising is a matter of both speed and trim. Mine will porpoise when I throttle back from WOT and don't trim it down. I'm guessing the sweet spot you are referring to is at WOT. I don't know there is one set spot on the trim for it. I think you have to find it every time out because every trip is probably a little different-a different partner that weighs more/less, different gear, etc. can change the weight of the boat so there may be a little variation in where the sweet spot is depending on the conditions. __________________ It's happened to the best of them: John 21:3

05-06-10, 11:25 PM	#11
carolina-rig-01 BassFishin.Com Premier Elite Join Date: Feb 2006 Location: Webb City, MO Posts: 6,387	It sounds to me like it is a motor height problem. Off the top of my head it sounds as if your motor is too low but the best thing to do is get the measurements and go from there. __________________ You only live once. But if you do it right, once is enough.

05-06-10, 07:55 AM	#2
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	UPDATE It appears as though the cav plate is 4-6 inches above the bottom of tho boat. Could this be why I'm having a problem?

05-06-10, 09:53 PM	#8
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	First, thanx all for your inpuit. I finaly feel as though I'm making progress on this problem. I do have a gauge and I know where about the gauge was right before it starts to porpoise. I'll take pics tommorrow in that position and all the way down and measure it as mississippiboy sugests......Stay tuned...... Remember, I cannot get it to that sweet spot due to the porpoising.

05-07-10, 08:56 AM	#13
Captmikestarrett BassFishin.Com Super Veteran Join Date: May 2006 Location: Accokeek MD Posts: 3,315	The top of the lower unit has a plate. That plate should be at waterline when running. Above it, it will porpoise. To far below it and it will porpoise on trim out. I had a Gambler with hydrulic lift plate and played with it up and down to figure out why it acted like it did. Capt Mike __________________ Capt Mike Starrett light tackle guide Potomac River http://www.indianheadcharters.com

05-07-10, 07:58 PM	#15
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Okay, I measured the distance of the center of the wheel to the bottom of the boat and the wheel is 5 3/4" below the bottom. When on plane, I can see the top of the hydrafoils. Also, the pitch on the prop is a 17. I could not replicate the position of the outboard when I was close to the best position. Also, someone earlier mention WOT. I usually dont run WOT, this occours at any speed, but I usually run @ 4,200 rpm and with this prop, thats puts me at about 28mph. Attached Thumbnails

05-07-10, 10:11 PM	#16
Bender BassFishin.Com Super Veteran Join Date: Jul 2005 Location: Brighton, MI Posts: 2,414	That sounds a bit too low, but I do not know that hull. Most average bassboats that I have messed with are somewhere between 2 1/2" to 3 1/2" below pad. Do you have a water pressure gauge? I realize without a jackplate you don't want to move it around a whole bunch to find out where it should be but I would take it up and watch the water pressure gauge, you don't want that to get low. I just looked through the Hydrasport Owner's List on BBC and the closest I can find to your boat is a guy running one at 4" below pad and his only bounces from 45-50. He had a fin on and that made it worse.

05-09-10, 03:16 PM	#18
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Update This motor is a long shaft, 20" I measure the transom @ 22" to the bottom of the boat I'm wondering if I w/b better off with a xtra long shaft 25"?

05-09-10, 04:46 PM	#19
lilmule BassFishin.Com Super Veteran Join Date: Feb 2010 Location: Buchanan,Tn Posts: 2,685	No your to deep now,propshaft about 3-3 1/2 under the pad with a stock gear case,porpoise is caused by excessive trim that low. Raising it the motor it will take less trim.Odds are with the motor at a less trim position running level it wont do it now even. And any motor should be run in the power band to insure long life,not exactly wot but in the band 4 to 4200 seems a tad low. When trimmed right the rooster tail behind the boat is no more than motor high,often less .

05-17-10, 06:15 AM	#21
1FASTLASER BassFishin.Com Super Veteran Join Date: Aug 2005 Location: crossett,arkansas Posts: 2,777	Ole carolina gets the cookie on the sweet spot.....the sweet spot will vary depending on load etc etc and will be close but not the same every time out. TAKES ALOT of seat time to figure it out. Second you need to get the prop shaft measurements and start there and as well take a look at the prop. Is the prop in good shape ???? You also need to realize that boat is underpowered. 90 hp on a 17ft boat is bare minimum. Porpising can be caused from a boat "trying to lift" but not having enough hp to sustain the lift.........most generally this is the cause. __________________ Laser's rule with Merc's doing the pushing..........KEEP THE WETSIDE DOWN AND THE DRY SIDE UP!!!!!!

05-17-10, 09:31 AM	#22
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Thanks for your input. to answer your questions; the prop sits about 5 1/2 below pad, the cav plate sits about 2" above pad, the prop is near new, no dings or dents. The prop is a Solas 13.25x17p and I also have a 4 blade 15p I use for pulling skiers and it does it as well. This boat max's out @ 32mph with WOT @ about 5,000. I hear what your saying about the 90, but I have had some corespondance with others with similar hulls and motor combinations and they dont report the problem and they report higher speeds. also, I had a Center console with a 90 on it, it was a heavy boat, double hull with flotation, and I had no porpoising and a top speed of 40mph. How does on test the output performance of an outboard on a bench? Is there a dyno for motors? So, although I agree it is on the lower end of power compared to most bass boats, I also think it should be doing better than this.

05-17-10, 10:09 AM	#23
lilmule BassFishin.Com Super Veteran Join Date: Feb 2010 Location: Buchanan,Tn Posts: 2,685	Simple solution raise the motor,a lil at a time,it should disappear,raising no higher than needed to go away it wont hurt the hole shot for pulling skiers With a 2-1 gear ratio,5000 rpm 17 P prop,slip ten percent speed should be right at 37mph. Check with those others getting more speed they arnt 5 1/2 under the pad,I bet. Its easier if on a jack plate if not go up one hole on the motor mounting.

05-17-10, 08:54 PM	#25
CABINDOC BassFishin.Com Member Join Date: May 2010 Location: New Egypt, NJ Posts: 18	Thanx both for your input. I agree and am going to try both. First the Hydrafoil, then the lift.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)