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Author Topic:   Porpoising

hval posted 11-14-2000 05:38 PM ET (US)
Recently purchased a 20' Outrage with 200 HP Johnson, both 1989. Problem, boat tends to porpoise when engine is not trimmed all the way down. Have heard that the installation of a Turbo-Lift fin on the engine cavation plate will eliminate problem and allow for trimming of boat.
Comments and or suggestions will be greatly appreciated..... Thanks
DIVE 1 posted 11-14-2000 07:44 PM ET (US)
We had the same problem with our BW. We installed Doel Fins and cured the problem.
Clark Roberts posted 11-15-2000 08:01 AM ET (US)
This problem (20' with V6 OMC) was discussed at length on a previous thread... bottom line revolved around engine weight and not enough "tuck-in" when trimmed down... a function of the engine bracketry design.. Doel-Fin will help, weight forward will help, wedges on engine bracketry will help, trim tabs will help... etc...etc... even the prop style can cause problems... try the doel-fin first along with moving some portable weight forward.. Good luck and happy Whalin'.. Clark... Spruce Creek Navy
jimh posted 11-15-2000 02:01 PM ET (US)
The earlier thread Clark refers to is here:
http://continuouswave.com/ubb/Forum4/HTML/000088.html .
For another data point, my 1987 20-Revenge is built on the same hull as your 1989 20-Outrage, and I notice that it will tend to bounce the bow if the engines are trimmed up too high in certain wave patterns.
But it just takes a bit of lower trim and the bow bounce goes away.
The smoother the water, the higher the engines may be trimmed before inducing any bouncing, it seems.
The Revenge comes with its own built in weight in the bow: the cuddy cabin superstructure. As a result, its ride characteristics may be different from a same-sized Outrage, which certainly must have less weight forward.
--jimh
jimh posted 11-15-2000 02:07 PM ET (US)
In the earlier discussion, the comment was made by Mike (Alioop):
"Engine installed height has a great effect on popoising. If the engine is too low the cavitation plate can cause the boat porpoise."
This raises the question: Where should the cavitation plate be when the boat is on plane?
In the water? Or out of the water? And how far?
--jimh
lhg posted 11-15-2000 03:01 PM ET (US)
In the earlier thread mentioned, both engine and boat were earlier models. I do not know if OMC improved the trim range of their engines during this period, but suspect they might have. In 1985 the 20' original (shallower Vee) Outrage hull was replaced with the deeper V model made from the 22' Outrage hull, a superior design.
So assuming the engine has additional "tuck under" capability, that is how the boat should be run. Whether the engine has additional trim-in capability may not matter, since ANY engine would need to be run at the same given angle to prevent porpoising. As long as this OMC can trim enough to prevent it is all that matters. If it can't, as in the other thread, then other steps have to be taken.
A 20' Outrage with 200HP should be reasonably fast, and most engine manufacturers recommend that under these top speed capabilities, the engine be raised on the transom one or two bolt holes from lowest possible position.
This means the anti-cavitation plate is running about 3/4" - 1 1/2" (max) above water surface when planing. So a bolt-on fin is not going to have any effect on planing performance, but nor will it contribute to increased drag. Many believe, however, that they help in getting the boat UP on plane, when the fin can be in contact with the water, in spite of the increased drag. A higher performance prop, such as a Merc "Mirage", "Laser" or "4 Blade Offshore" should probably be used. (They will fit OMC engines- see mercurymarine.com). These props all have agressive holding capabilites, needed for the higher mounting height. Top speed will increase by 2 or 3 MPH, and handling stability will improve due to less drag from the lower unit.
Alioop posted 11-15-2000 07:13 PM ET (US)
When I posted that post I should have explained it more than I did.If the cavitation plate is to low in the water and you trim your motor out porposing is caused by a teatertottering effect between the bow and the cavitation plate.(This why a doel-fin can change this condition,by adding a doel-fin you increase the size of the plate) Raising the engine moves the plate upwards and changes the effective angle and allows more trim to be used before the tettertottering can take effect. Mike
OutrageMan posted 11-16-2000 08:04 PM ET (US)
I did mention in the other thread that I did install a fin on my '91 22' Outrage with whaler drive and a 250hp Yamaha.
I can not speak highly enough of this mod. It actually allows me to use the trim, and has improved an already great ride.
Bottom line, it was the best $35 I have ever spent.
If you want a second opinion, Russ - Ephraimwhaler - has been on my boat and also owns a 22. He can attest to it being a great mod.
Brian
hval posted 11-19-2000 06:52 PM ET (US)
To all who responded to my inquiry regarding porpoising... thank you. I will apply your suggestions this coming season. Best wishes to all for the coming holiday season and good boating.

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Author	Topic: Porpoising
hval	posted 11-14-2000 05:38 PM ET (US) Recently purchased a 20' Outrage with 200 HP Johnson, both 1989. Problem, boat tends to porpoise when engine is not trimmed all the way down. Have heard that the installation of a Turbo-Lift fin on the engine cavation plate will eliminate problem and allow for trimming of boat. Comments and or suggestions will be greatly appreciated..... Thanks
DIVE 1	posted 11-14-2000 07:44 PM ET (US) We had the same problem with our BW. We installed Doel Fins and cured the problem.
Clark Roberts	posted 11-15-2000 08:01 AM ET (US) This problem (20' with V6 OMC) was discussed at length on a previous thread... bottom line revolved around engine weight and not enough "tuck-in" when trimmed down... a function of the engine bracketry design.. Doel-Fin will help, weight forward will help, wedges on engine bracketry will help, trim tabs will help... etc...etc... even the prop style can cause problems... try the doel-fin first along with moving some portable weight forward.. Good luck and happy Whalin'.. Clark... Spruce Creek Navy
jimh	posted 11-15-2000 02:01 PM ET (US) The earlier thread Clark refers to is here: http://continuouswave.com/ubb/Forum4/HTML/000088.html . For another data point, my 1987 20-Revenge is built on the same hull as your 1989 20-Outrage, and I notice that it will tend to bounce the bow if the engines are trimmed up too high in certain wave patterns. But it just takes a bit of lower trim and the bow bounce goes away. The smoother the water, the higher the engines may be trimmed before inducing any bouncing, it seems. The Revenge comes with its own built in weight in the bow: the cuddy cabin superstructure. As a result, its ride characteristics may be different from a same-sized Outrage, which certainly must have less weight forward. --jimh
jimh	posted 11-15-2000 02:07 PM ET (US) In the earlier discussion, the comment was made by Mike (Alioop): "Engine installed height has a great effect on popoising. If the engine is too low the cavitation plate can cause the boat porpoise." This raises the question: Where should the cavitation plate be when the boat is on plane? In the water? Or out of the water? And how far? --jimh
lhg	posted 11-15-2000 03:01 PM ET (US) In the earlier thread mentioned, both engine and boat were earlier models. I do not know if OMC improved the trim range of their engines during this period, but suspect they might have. In 1985 the 20' original (shallower Vee) Outrage hull was replaced with the deeper V model made from the 22' Outrage hull, a superior design. So assuming the engine has additional "tuck under" capability, that is how the boat should be run. Whether the engine has additional trim-in capability may not matter, since ANY engine would need to be run at the same given angle to prevent porpoising. As long as this OMC can trim enough to prevent it is all that matters. If it can't, as in the other thread, then other steps have to be taken. A 20' Outrage with 200HP should be reasonably fast, and most engine manufacturers recommend that under these top speed capabilities, the engine be raised on the transom one or two bolt holes from lowest possible position. This means the anti-cavitation plate is running about 3/4" - 1 1/2" (max) above water surface when planing. So a bolt-on fin is not going to have any effect on planing performance, but nor will it contribute to increased drag. Many believe, however, that they help in getting the boat UP on plane, when the fin can be in contact with the water, in spite of the increased drag. A higher performance prop, such as a Merc "Mirage", "Laser" or "4 Blade Offshore" should probably be used. (They will fit OMC engines- see mercurymarine.com). These props all have agressive holding capabilites, needed for the higher mounting height. Top speed will increase by 2 or 3 MPH, and handling stability will improve due to less drag from the lower unit.
Alioop	posted 11-15-2000 07:13 PM ET (US) When I posted that post I should have explained it more than I did.If the cavitation plate is to low in the water and you trim your motor out porposing is caused by a teatertottering effect between the bow and the cavitation plate.(This why a doel-fin can change this condition,by adding a doel-fin you increase the size of the plate) Raising the engine moves the plate upwards and changes the effective angle and allows more trim to be used before the tettertottering can take effect. Mike
OutrageMan	posted 11-16-2000 08:04 PM ET (US) I did mention in the other thread that I did install a fin on my '91 22' Outrage with whaler drive and a 250hp Yamaha. I can not speak highly enough of this mod. It actually allows me to use the trim, and has improved an already great ride. Bottom line, it was the best $35 I have ever spent. If you want a second opinion, Russ - Ephraimwhaler - has been on my boat and also owns a 22. He can attest to it being a great mod. Brian
hval	posted 11-19-2000 06:52 PM ET (US) To all who responded to my inquiry regarding porpoising... thank you. I will apply your suggestions this coming season. Best wishes to all for the coming holiday season and good boating.