Anonymous
01-17-2003, 01:26 AM
MarkG
normal member in standard member. 1. Prop cavitation and fishtailing in steep following seas
Has anyone else had problems with keeping steerage in short period, steep following seas ? My 220 Predator has a tendency to lose steerage and cavitate in rough, steep following seas, especially if there is an aft quarter component. The only thing that ssems to help is slowing down and pulling the bow up which then makes for a long, slow ride home.
I attribute it to my small, quickly spinning prop (14x10) and rudder and was wondering if anyone has any advice on dealing with this problem.
Date: 12:58 p.m. on 09-26-2000
Leprechaun
normal member in standard member. 2. Re:Prop cavitation and fishtailing in steep following seas
Mark - How big a sea and how much do you slow down? Every boat has problems in these conditions. With my 26 - over a true 4' ocean - if they are close-spaced - meaning less than a boat's length or so between peaks, I too slow way down and put the nose up. What else can you do? If they're wide spaced then I can balance off the trim and go like hell - did it last winter a few times coming home from Jersey - big ocean - maybe true 6-7 footers but they were dead aft and I was able to kick up the response setting on the pilot and just blow home to Long Island. It was kind of cool to see/feel the wave pick up the stern and try to spin it, only to have the pilot immediately kick the rudder and re-straighten the boat. Scared the hell out of the guys in the cockpit but no problem - made a true 19 mph thru some really big waves. Its all in how far apart they are. A Shammie can climb up thier backs with its sharp, deep entry and surf down thier front side on its flat rear quarters. As long as you watch yourself, a rear quartering sea is only marginally painful - the keel and extreme forward bouyancy built into a Shamrock will help prevent broaching, unlike some big-name boats like the Henriques 35 and the Bruno&Stillman 36, both of which are absolutely horrible under these conditions. Give credit to Shamrock's marine engingeer, who ever he was. He got these hulls just about perfect. If you want to knit-pick - they could use a bit more bow flair though. Leprechaun
Date: 04:53 p.m. on 09-26-2000
MarkG
normal member in standard member. 3. Re:Re:Prop cavitation and fishtailing in steep following seas
Lep,
Thanks for the reply.
This past weekend we ran about 26 miles back home and the seas were about 3-4' every 6-7 seconds. I was able to keep going about 15 knots but it was a lot of work on steering and the throttle w/ a few bad cavitations. In larger period swell, no problem except I somtimes have to push the throttle forward a bit to get over the back of large swells.
The prop really seems to be prone to cavitation in rough, rear quartering seas, even in 2' wind chop.
Date: 05:13 p.m. on 09-26-2000
Leprechaun
normal member in standard member. 4. Re:Prop cavitation and fishtailing in steep following seas
My Pred 26 will also break the prop loose once in a while in a bad ocean - no biggie - but you say you cav in a TWO foot sea? That doesn't sound right. Do you happen to know if your 14X10 prop is the factory installed size? Sounds very undersquare to me, but maybe you have a direct-drive 1:1 trans - that is, no reduction? Leprechaun
Date: 07:16 p.m. on 09-26-2000
MarkG
normal member in standard member. 5. Re:Re:Prop cavitation and fishtailing in steep following seas
Yes my drive is 1:1 resulting in some high tip speeds. Seas may have been 3-4 but the small side chop combined w/ swell seems to really cause the cavitation (maybe once every 20 minutes). Sounds like the 26 is a better ride like most other makes.
mg
Date: 08:48 p.m. on 09-26-2000
Capt_Dog
normal member in standard member. 6. Re:Prop cavitation and fishtailing in steep following seas
Nothing is quite as unnerving as what you describe in a boat. I have spent many days on sailboats and can tell you it happens all too often in those animals. However, I think it is for the same reason. Shamrocks' strength lies in its lower and centralized center of gravity, much like a sailboat with a keel in the center. This makes for a stable boat in slow trolling conditions (and thankGod for it). It also makes for the perfect pivot point for turning. If you have cut your teeth in outboard boats then the pivot point is generally in the aft third of the boat if not further back, much like an automobile.
So what? Well when you decelerate into the back of the way in front (generally after surfing down the face of the aft wave) the pivot point and righting moment shift forward and can lift the transom. Moreover, it takes water off of the rudder and steerage is lost. The boat will tend to dig into the back of that same wave and rotate and try to run down the trough. Bad deal. You then get water back across the rudder then you wrestle the boat back into position to surf down the next one.
The only relief to this issue is to use the speed from the surf to climb the back while easing the throttle. This keeps the deceleration down to a minimum. This is very effective in very large seas. In small seas 2-4, like you mention, resist steering and throttle inputs at all. This sounds crazy however, when the boat decelerates and begins its rotation do nothing. Much like Leprechaun mentions his AutoPilot doing, it makes small, and completely unemotional, steering changes. The only problem with real human inputs is that we are using the steering wheel as a handle and are very emotional during the action and tend to over correct.
I hope this helps. I chased (my term for the constant input of steering and throttle due to following seas)a 26' Glacier Bay Power Catamaran around the Atlantic ocean for two seasons until I finally trusted my autopilot enough to leave it alone. Then I watched that damn machine do what I could not do, leave the emotions out of the helm. My Shamrock does this exact thing everytime I return on an outgoing tide through the jetties. Three foot and 15' apart, nasty and comletely manageable. Good Luck. Lee
Date: 11:25 p.m. on 09-26-2000
Gavin
7. Re:Re:Prop cavitation and fishtailing in steep following seas
--------------------------------------------------------------------------------
Capt_Dog (09-26-2000 11:25 p.m.):
Nothing is quite as unnerving as what you describe in a boat. I have spent many days on sailboats and can tell you it happens all too often in those animals. However, I think it is for the same reason. Shamrocks' strength lies in its lower and centralized center of gravity, much like a sailboat with a keel in the center. This makes for a stable boat in slow trolling conditions (and thankGod for it). It also makes for the perfect pivot point for turning. If you have cut your teeth in outboard boats then the pivot point is generally in the aft third of the boat if not further back, much like an automobile.
So what? Well when you decelerate into the back of the way in front (generally after surfing down the face of the aft wave) the pivot point and righting moment shift forward and can lift the transom. Moreover, it takes water off of the rudder and steerage is lost. The boat will tend to dig into the back of that same wave and rotate and try to run down the trough. Bad deal. You then get water back across the rudder then you wrestle the boat back into position to surf down the next one.
The only relief to this issue is to use the speed from the surf to climb the back while easing the throttle. This keeps the deceleration down to a minimum. This is very effective in very large seas. In small seas 2-4, like you mention, resist steering and throttle inputs at all. This sounds crazy however, when the boat decelerates and begins its rotation do nothing. Much like Leprechaun mentions his AutoPilot doing, it makes small, and completely unemotional, steering changes. The only problem with real human inputs is that we are using the steering wheel as a handle and are very emotional during the action and tend to over correct.
I hope this helps. I chased (my term for the constant input of steering and throttle due to following seas)a 26' Glacier Bay Power Catamaran around the Atlantic ocean for two seasons until I finally trusted my autopilot enough to leave it alone. Then I watched that damn machine do what I could not do, leave the emotions out of the helm. My Shamrock does this exact thing everytime I return on an outgoing tide through the jetties. Three foot and 15' apart, nasty and comletely manageable. Good Luck. Lee
--------------------------------------------------------------------------------
Nice post Lee! Do come back and share your
knowledge. It is certainly appreciated and
truly at the core of what I hope to make this board into.. A great site to share ideas and thoughts about Shamrock boats!
Thank you. Gavin
Date: 01:48 a.m. on 09-27-2000
clydew
8. Re:Prop cavitation and fishtailing in steep following seas
Mark, I know the feeling. Came in yesterday with a following sea (maybe 4-5 ft) and more than once I thought the boat was gonna make a sharp turn without any imput by me. I'm new with this Shamrock thing, but I finally figured out that holding onto the wheel securely and making small imputs seemed to make for a nice ride home. BTW the tach was at 3000 rpm and the boat was plainning nicely. No speedo on board so not sure how fast I was going.
Clyde
Date: 01:02 p.m. on 09-27-2000
mtidaho
9. Re:Re:Prop cavitation and fishtailing in steep following seas
Mark, don't feel like the lone irishman.
On my way back from Florida with a 22 SE open fish...stopped in Wisconsin to visit, wash the salt off and do a maiden voyage. And I was also in some high wind driven chop from the rear quarter which caused some cavitation. I was a bit surprised because there was no wave action just 2-3 foot chop..I chalked it up to my inexperience. If the Leprechaun is doing his usual good job of monitoring this site...all these post about props and caused me to crawl under my Shammy and take a look. "93 14LH ll"
what does that mean. 14 inch--left hand?
Did get the boat all winterized.
my thanks to all you great hands who share your knowledge.
mtidaho
Date: 11:06 p.m. on 10-09-2000
Leprechaun
normal member in standard member. 10. Re:Re:Re:Prop cavitation and fishtailing in steep following seas
--------------------------------------------------------------------------------
mtidaho (10-09-2000 11:06 p.m.):
Mark, don't feel like the lone irishman.
On my way back from Florida with a 22 SE open fish...stopped in Wisconsin to visit, wash the salt off and do a maiden voyage. And I was also in some high wind driven chop from the rear quarter which caused some cavitation. I was a bit surprised because there was no wave action just 2-3 foot chop..I chalked it up to my inexperience. If the Leprechaun is doing his usual good job of monitoring this site...all these post about props and caused me to crawl under my Shammy and take a look. "93 14LH ll"
what does that mean. 14 inch--left hand?
Did get the boat all winterized.
my thanks to all you great hands who share your knowledge.
mtidaho
--------------------------------------------------------------------------------
mt - not real sure what the prop manufacturer hadi mind - I can only partially translate - Its a 14" Diameter, Left Handed prop (As most "Standard Rotation" single screw boats are) and eith its got an 11" pitch or maybe the "II" means "Square?", meaning 14x14? Call Shamrock, er, Kcs and ask what the factory installed prop is. Then let us know and it'll add to our sum knowledge of "Prop Vodoo". Leprechaun
Date: 04:54 p.m. on 10-10-2000
MarkG
normal member in standard member. 11. Re:Re:Re:Prop cavitation and fishtailing in steep following seas
That would be a 14" diameter x 11" pitch left hand prop which is the exact same prop my '91 220 Predator came with. I later repitched it to 10".
normal member in standard member. 1. Prop cavitation and fishtailing in steep following seas
Has anyone else had problems with keeping steerage in short period, steep following seas ? My 220 Predator has a tendency to lose steerage and cavitate in rough, steep following seas, especially if there is an aft quarter component. The only thing that ssems to help is slowing down and pulling the bow up which then makes for a long, slow ride home.
I attribute it to my small, quickly spinning prop (14x10) and rudder and was wondering if anyone has any advice on dealing with this problem.
Date: 12:58 p.m. on 09-26-2000
Leprechaun
normal member in standard member. 2. Re:Prop cavitation and fishtailing in steep following seas
Mark - How big a sea and how much do you slow down? Every boat has problems in these conditions. With my 26 - over a true 4' ocean - if they are close-spaced - meaning less than a boat's length or so between peaks, I too slow way down and put the nose up. What else can you do? If they're wide spaced then I can balance off the trim and go like hell - did it last winter a few times coming home from Jersey - big ocean - maybe true 6-7 footers but they were dead aft and I was able to kick up the response setting on the pilot and just blow home to Long Island. It was kind of cool to see/feel the wave pick up the stern and try to spin it, only to have the pilot immediately kick the rudder and re-straighten the boat. Scared the hell out of the guys in the cockpit but no problem - made a true 19 mph thru some really big waves. Its all in how far apart they are. A Shammie can climb up thier backs with its sharp, deep entry and surf down thier front side on its flat rear quarters. As long as you watch yourself, a rear quartering sea is only marginally painful - the keel and extreme forward bouyancy built into a Shamrock will help prevent broaching, unlike some big-name boats like the Henriques 35 and the Bruno&Stillman 36, both of which are absolutely horrible under these conditions. Give credit to Shamrock's marine engingeer, who ever he was. He got these hulls just about perfect. If you want to knit-pick - they could use a bit more bow flair though. Leprechaun
Date: 04:53 p.m. on 09-26-2000
MarkG
normal member in standard member. 3. Re:Re:Prop cavitation and fishtailing in steep following seas
Lep,
Thanks for the reply.
This past weekend we ran about 26 miles back home and the seas were about 3-4' every 6-7 seconds. I was able to keep going about 15 knots but it was a lot of work on steering and the throttle w/ a few bad cavitations. In larger period swell, no problem except I somtimes have to push the throttle forward a bit to get over the back of large swells.
The prop really seems to be prone to cavitation in rough, rear quartering seas, even in 2' wind chop.
Date: 05:13 p.m. on 09-26-2000
Leprechaun
normal member in standard member. 4. Re:Prop cavitation and fishtailing in steep following seas
My Pred 26 will also break the prop loose once in a while in a bad ocean - no biggie - but you say you cav in a TWO foot sea? That doesn't sound right. Do you happen to know if your 14X10 prop is the factory installed size? Sounds very undersquare to me, but maybe you have a direct-drive 1:1 trans - that is, no reduction? Leprechaun
Date: 07:16 p.m. on 09-26-2000
MarkG
normal member in standard member. 5. Re:Re:Prop cavitation and fishtailing in steep following seas
Yes my drive is 1:1 resulting in some high tip speeds. Seas may have been 3-4 but the small side chop combined w/ swell seems to really cause the cavitation (maybe once every 20 minutes). Sounds like the 26 is a better ride like most other makes.
mg
Date: 08:48 p.m. on 09-26-2000
Capt_Dog
normal member in standard member. 6. Re:Prop cavitation and fishtailing in steep following seas
Nothing is quite as unnerving as what you describe in a boat. I have spent many days on sailboats and can tell you it happens all too often in those animals. However, I think it is for the same reason. Shamrocks' strength lies in its lower and centralized center of gravity, much like a sailboat with a keel in the center. This makes for a stable boat in slow trolling conditions (and thankGod for it). It also makes for the perfect pivot point for turning. If you have cut your teeth in outboard boats then the pivot point is generally in the aft third of the boat if not further back, much like an automobile.
So what? Well when you decelerate into the back of the way in front (generally after surfing down the face of the aft wave) the pivot point and righting moment shift forward and can lift the transom. Moreover, it takes water off of the rudder and steerage is lost. The boat will tend to dig into the back of that same wave and rotate and try to run down the trough. Bad deal. You then get water back across the rudder then you wrestle the boat back into position to surf down the next one.
The only relief to this issue is to use the speed from the surf to climb the back while easing the throttle. This keeps the deceleration down to a minimum. This is very effective in very large seas. In small seas 2-4, like you mention, resist steering and throttle inputs at all. This sounds crazy however, when the boat decelerates and begins its rotation do nothing. Much like Leprechaun mentions his AutoPilot doing, it makes small, and completely unemotional, steering changes. The only problem with real human inputs is that we are using the steering wheel as a handle and are very emotional during the action and tend to over correct.
I hope this helps. I chased (my term for the constant input of steering and throttle due to following seas)a 26' Glacier Bay Power Catamaran around the Atlantic ocean for two seasons until I finally trusted my autopilot enough to leave it alone. Then I watched that damn machine do what I could not do, leave the emotions out of the helm. My Shamrock does this exact thing everytime I return on an outgoing tide through the jetties. Three foot and 15' apart, nasty and comletely manageable. Good Luck. Lee
Date: 11:25 p.m. on 09-26-2000
Gavin
7. Re:Re:Prop cavitation and fishtailing in steep following seas
--------------------------------------------------------------------------------
Capt_Dog (09-26-2000 11:25 p.m.):
Nothing is quite as unnerving as what you describe in a boat. I have spent many days on sailboats and can tell you it happens all too often in those animals. However, I think it is for the same reason. Shamrocks' strength lies in its lower and centralized center of gravity, much like a sailboat with a keel in the center. This makes for a stable boat in slow trolling conditions (and thankGod for it). It also makes for the perfect pivot point for turning. If you have cut your teeth in outboard boats then the pivot point is generally in the aft third of the boat if not further back, much like an automobile.
So what? Well when you decelerate into the back of the way in front (generally after surfing down the face of the aft wave) the pivot point and righting moment shift forward and can lift the transom. Moreover, it takes water off of the rudder and steerage is lost. The boat will tend to dig into the back of that same wave and rotate and try to run down the trough. Bad deal. You then get water back across the rudder then you wrestle the boat back into position to surf down the next one.
The only relief to this issue is to use the speed from the surf to climb the back while easing the throttle. This keeps the deceleration down to a minimum. This is very effective in very large seas. In small seas 2-4, like you mention, resist steering and throttle inputs at all. This sounds crazy however, when the boat decelerates and begins its rotation do nothing. Much like Leprechaun mentions his AutoPilot doing, it makes small, and completely unemotional, steering changes. The only problem with real human inputs is that we are using the steering wheel as a handle and are very emotional during the action and tend to over correct.
I hope this helps. I chased (my term for the constant input of steering and throttle due to following seas)a 26' Glacier Bay Power Catamaran around the Atlantic ocean for two seasons until I finally trusted my autopilot enough to leave it alone. Then I watched that damn machine do what I could not do, leave the emotions out of the helm. My Shamrock does this exact thing everytime I return on an outgoing tide through the jetties. Three foot and 15' apart, nasty and comletely manageable. Good Luck. Lee
--------------------------------------------------------------------------------
Nice post Lee! Do come back and share your
knowledge. It is certainly appreciated and
truly at the core of what I hope to make this board into.. A great site to share ideas and thoughts about Shamrock boats!
Thank you. Gavin
Date: 01:48 a.m. on 09-27-2000
clydew
8. Re:Prop cavitation and fishtailing in steep following seas
Mark, I know the feeling. Came in yesterday with a following sea (maybe 4-5 ft) and more than once I thought the boat was gonna make a sharp turn without any imput by me. I'm new with this Shamrock thing, but I finally figured out that holding onto the wheel securely and making small imputs seemed to make for a nice ride home. BTW the tach was at 3000 rpm and the boat was plainning nicely. No speedo on board so not sure how fast I was going.
Clyde
Date: 01:02 p.m. on 09-27-2000
mtidaho
9. Re:Re:Prop cavitation and fishtailing in steep following seas
Mark, don't feel like the lone irishman.
On my way back from Florida with a 22 SE open fish...stopped in Wisconsin to visit, wash the salt off and do a maiden voyage. And I was also in some high wind driven chop from the rear quarter which caused some cavitation. I was a bit surprised because there was no wave action just 2-3 foot chop..I chalked it up to my inexperience. If the Leprechaun is doing his usual good job of monitoring this site...all these post about props and caused me to crawl under my Shammy and take a look. "93 14LH ll"
what does that mean. 14 inch--left hand?
Did get the boat all winterized.
my thanks to all you great hands who share your knowledge.
mtidaho
Date: 11:06 p.m. on 10-09-2000
Leprechaun
normal member in standard member. 10. Re:Re:Re:Prop cavitation and fishtailing in steep following seas
--------------------------------------------------------------------------------
mtidaho (10-09-2000 11:06 p.m.):
Mark, don't feel like the lone irishman.
On my way back from Florida with a 22 SE open fish...stopped in Wisconsin to visit, wash the salt off and do a maiden voyage. And I was also in some high wind driven chop from the rear quarter which caused some cavitation. I was a bit surprised because there was no wave action just 2-3 foot chop..I chalked it up to my inexperience. If the Leprechaun is doing his usual good job of monitoring this site...all these post about props and caused me to crawl under my Shammy and take a look. "93 14LH ll"
what does that mean. 14 inch--left hand?
Did get the boat all winterized.
my thanks to all you great hands who share your knowledge.
mtidaho
--------------------------------------------------------------------------------
mt - not real sure what the prop manufacturer hadi mind - I can only partially translate - Its a 14" Diameter, Left Handed prop (As most "Standard Rotation" single screw boats are) and eith its got an 11" pitch or maybe the "II" means "Square?", meaning 14x14? Call Shamrock, er, Kcs and ask what the factory installed prop is. Then let us know and it'll add to our sum knowledge of "Prop Vodoo". Leprechaun
Date: 04:54 p.m. on 10-10-2000
MarkG
normal member in standard member. 11. Re:Re:Re:Prop cavitation and fishtailing in steep following seas
That would be a 14" diameter x 11" pitch left hand prop which is the exact same prop my '91 220 Predator came with. I later repitched it to 10".