Boat lists,porposes while on plane.

[Tail_Gunner]

At this point know one know's, it will be revealing to you as you start with a high engine height and start down. Bass boat's high HP do quite well with that kind of combo...setback's are common big motor's are common just not the tunnel....they also run run the engine quite high the reason for the setback. I believe you have the boat set up improperly...engine height and the wrong prop rev 4's are know to run well with a deep drive aka I/O's...By design a your hull is meant to skip over the water no plow like a deep v...now combine that with a drive that is running to deep a prop that is a known lifter..high horse power and a fairly light boat and all kinds of thing's can happen.

One big thing you could do is get a hold of a cheap 3blade alum prop about 3 pitches up from that rev4 and start with that instead of the 4blade ss. I dont think you have a hook going on but we shall see.

 

[juicegoose]

Thanks Guys.
Kind of a side story but when I originally bought the boat it had a 10" jackplate on her and a 21p powertech ofs3 prop. It also had both house and cranking batteries in the rear. I noticed quickly after trying to get used to her that the boat would porpose some and blow out in turns, any turn. Upon further inspection of the prop I came to realization that the powertech prop was missing nearly an inch of diameter and the shape of the blade was no longer a big elephant ear and instead more to a point on the tip. I of course had no trouble getting out of the water with this worn out prop but the slip was crazy. With T top on, running 5500-5600 rpm I could clock almost 50mph. I keep that prop as a backup on the boat. After realizing I had porpose issues and needing to add a trolling motor I relocated as much weight as I could forward. I moved all batteries to the center console I now have 4 batteries in there. That's a lot of weight in the center of the boat. I also located a 6" jackplate and replaced the 10" jackplate with the 6".
While on a straight run I have tested and can run the motor all the way up to 6". As high as it will jack the motor and I still don't loose water pressure or begin to blow out.
I have a local prop guy(very well respected and does work on all manor of boats) that I have spoken with (of course after buying the rev4 doh!!) and he stated just like everyone here that the rev4 is the wrong prop for my boat. He recommended a 19p 3 blade. Can't remember the name of the manufacture but the model number was similar to powertech. After doing all this testing I plan on bringing the rev4 back with me and trying out some props through him. He has a great policy on prop testing until I get what I want out of the boat, within reason of course.

 

[alldodge]

Thanks Guys.
Kind of a side story but when I originally bought the boat it had a 10" jackplate on her and a 21p powertech ofs3 prop. It also had both house and cranking batteries in the rear. I noticed quickly after trying to get used to her that the boat would porpose some and blow out in turns, any turn. Upon further inspection of the prop I came to realization that the powertech prop was missing nearly an inch of diameter and the shape of the blade was no longer a big elephant ear and instead more to a point on the tip. I of course had no trouble getting out of the water with this worn out prop but the slip was crazy. With T top on, running 5500-5600 rpm I could clock almost 50mph. I keep that prop as a backup on the boat. After realizing I had porpose issues and needing to add a trolling motor I relocated as much weight as I could forward. I moved all batteries to the center console I now have 4 batteries in there. That's a lot of weight in the center of the boat. I also located a 6" jackplate and replaced the 10" jackplate with the 6".
While on a straight run I have tested and can run the motor all the way up to 6". As high as it will jack the motor and I still don't loose water pressure or begin to blow out.
I have a local prop guy(very well respected and does work on all manor of boats) that I have spoken with (of course after buying the rev4 doh!!) and he stated just like everyone here that the rev4 is the wrong prop for my boat. He recommended a 19p 3 blade. Can't remember the name of the manufacture but the model number was similar to powertech. After doing all this testing I plan on bringing the rev4 back with me and trying out some props through him. He has a great policy on prop testing until I get what I want out of the boat, within reason of course.

You had porpoise issues with a 10 inch so you moved stuff forward along with moving the engine 4 inched forward. Moving the engine forward moves the center of gravity forward. The porpoise effect should not happen with raising or lowing the plate, it should happen with trimming out. Maybe move the batteries back to the stern area. Getting more weight on the stern will allow more trim. Or may need to figure how the engine can be tucked under the boat more

Edit: scratch that stuff on my comments in bold, you need to get less weight off the stern and more toward the bow. Seems this happens most often with CC and large engines. Have you tied it without the jack plate?

 

[Tail_Gunner]

The boat has done this since I've bought it. When I test drove it the original owner wasn't comfortable letting someone else drive it. I didn't think anything of it as I would kinda feel the same way. The original prop on the boat was a powertech 3 blade 21p. It kept blowing out and when I brought it in for service the guy showed me what the diameter should have been. Literally an 1" of prop was gone. Even with that prop and before I got trim tabs the boat listed slightly to port and would porpose. I could 50mph out of her wide open though at 5500 rpm.

Tail gunner the V on that hull actually stops right at the center console and then the pocket tunnel starts a reverse angle back up to the keep.

Bondo.
When you say motor in neutral trim do you mind explaining?

Thanks guys for all your help I really appreciate it. I've loved the fishability of the boat but this porposing is annoying.

Here's a key: Tail gunner the V on that hull actually stops right at ....center console........ and then the pocket tunnel starts a reverse angle back up to the keep

I moved all batteries to the .......center console......... I now have 4 batteries in there. That's a lot of weight in the center of the boat. I


If I read this right you have the weight on the beginning of the tunnel when it should be evenly distributed on each side of the sponson's and more toward's the transom area. You want the weight evenly dist on the largest running surface. The way it is setup now you have the engine pulling up the bow and she fall's off creating the bouncing...Smiles you may very well need to setback the engine again to 10".....that would place a large center of mass directly over the longest widest portion of the sponson's and with a three blade you wont has as much stern lift fighting the balance and that motor prop combo there is a lot going on...

 

[juicegoose]

I know for sure that switching over to the 6" helped some in this issue. The boat has two seats in the rear and often times passengers sit there. It hasn't helped or hurt the effect and they are sitting right over where the batteries were.

 

[alldodge]

What happens when folks are on the bow?

 

[juicegoose]

It obviously helps some but I have no avenue to put more weight forward.

I think I might have stumbled on part of my problem though. I have a lot of time riding on boats but not a ton of years driving them. I think I might be trimming out incorrectly.
I was always taught that to trim out your boat properly or know you've got it right for cruise you should do the following.
From idle, push the throttle forward with the motor tucked in until the boat has pushed over and is now on plane.
Once on plane begin untucking the motor and accelerating until desired cruise speed is obtained. Keeping an eye on the feel of the steering continue to untuck the motor until the steering force left and right feels roughly equal. Then trim back down a little.

That is what I'm trying to chase. I can tuck the motor under to not porpoise but doing so makes it hard to turn port. Trim tabs has helped as it has allowed me to introduce the trim tabs to counteract the porpoise at high trim angles. But introducing the trim tabs takes away from speed.

Am I wrong?

 

[alldodge]

Trim should have little or no effect with full hydraulic steering. Check the fluid level at the helm and see if it is full

Take off as you say and once on plane trim up until the boat starts to porpoise, then bring back down until it stops, this is optimum for the speed your going. If you increase or decrease speed, trim will need to be readjusted in the same fashion. Now this works with all boats, only caveat I'll say is I have never driven a CC with a tunnel, so I cannot say with certainty that this will or will not change the outcome.

 

[juicegoose]

what about the felt steering pressure?

 

[alldodge]

what about the felt steering pressure?

It should not be there or next to none if your steering is working properly. If the hydraulic steering reservoir is low you will feel the torque. Either way more or less trim should not be used for feeling the torque or not. Trim changes the bow angle, tabs changes list. Don't know if your engine has an anode on the bottom of the ventilation plate, but if it does and you have room for a zinc torque type anode, it could be used

 

[Scott Danforth]

^ +1. steering feel and proper hull attitude are not directly related. the steering feel is a separate issue. the proper way to trim is in response #48 by AllDodge.

trim all the way in for the hole shot, start trimming up as it climbs out the hole. if you start to porpoise, you have trimmed up too much, back 'er down a bit

 

[juicegoose]

Thanks Scott to the bottom line is that I can trim to a point of porpoise trim back in and still have it harder to steer port then starboard. As far as the anode goes I was told the larger mercs wit hydraulic steerings don't need the tab as it doesn't help

 

[Tail_Gunner]

id be willing to bet your 2/4" to deep

 

[juicegoose]

Hey hey i there is a picture of the ole girl. That was withthe old powertech ofs3 wore out prop. Also its hard to tell where the jackplate was positioned in that picture. I'll make sure to take some photos at all the positions.
Im kinda feeling better at the moment that some of my porposing might have been being caused by my false assumption that a properly trimmed motor should be easy to steer both directions.

 

[Barramundi NQ]

Hey juice. Hydraulic steering should have almost zero torque steer, at least YOU shouldn't be ABLE to feel the torque generated at the helm..... After reading the whole thread, I'm leaning towards the jackplatebeing the problem and the maybe a hook in the hull. I've never seen a boat list as a result of torque.....wet foam??? (does it sit perfectly level at rest?) Remember that the 200hp is only 200hp at full throttle. So if overpowered is the problem 3/4 throttle should settle it down At 3/4 throttle it might be generating 150-175hp??? (just guessing).
IMHO setting the Jack plate height at the ramp, by that I mean fully tucked in and cavitation plate level with the keels either side of the tunnel, trim tabs fully up, then drive it and only adjust the trim whilst underway and watch what happens. I personally trim my engine once I'm on the plane until it starts to cavitate then back in a touch or 2. Same drama? try setting it to the top of the tunnel height and try again.
My 2c worth...

 

[juicegoose]

NQ thanks for the tips. After contacting seastar your right i need to make sure the system is purged and possibly repair the helm check valve. Im not sure the listing from wet foam. Anyway to check that?

 

[Tail_Gunner]

Hey hey i there is a picture of the ole girl. That was withthe old powertech ofs3 wore out prop. Also its hard to tell where the jackplate was positioned in that picture. I'll make sure to take some photos at all the positions.
Im kinda feeling better at the moment that some of my porposing might have been being caused by my false assumption that a properly trimmed motor should be easy to steer both directions.

I think your going to find a very narrow range of trim on your boat primarily due to high horse power..it really depends how much of a tunnel you have going there.

http://www.aeromarineresearch.com/download/TBPNews/tbpnews144.html

http://boatdesign.net/articles/tunnel-hull-design/

http://www.aeromarineresearch.com/pu...R_Feb2013.html

 

[juicegoose]

Thanks for the articles gunner. My tunnel isnt a full on tunnel boat i think they call mine a pocket tunnel. Essentially its a v hull until just after the lowest portion of V in the water. I think some of the same dynamics apply though

 

[Fed]

When your driving along some interesting things happen...

1) Your boat is moving forwards, this is a good thing.

2) When viewed from above your outboard motor is trying to spin anti-clockwise because the crankshaft is trying to spin clockwise, this is countered by external water pressure on the torque tab. Without the torque tab this force is transmitted to the hull via the steering.

3) When viewed from behind your hull is trying to spin anti-clockwise because the prop is spinning clockwise, this is countered by the hull in the water.

The key point so far is external water pressure on the torque tab, a force from outside the boat.

Now the trim...

1) When viewed from behind too much negative trim loads the right hand prop blade and unloads the left hand blade/s causing the boat to try & turn to the Starboard.

2) When viewed from behind too much positive trim loads the left hand prop blade and unloads the right hand blade/s causing the boat to try & turn to the Port.

3) Neutral trim (AV plate parallel to the water surface) equalizes these forces.

As you can see you have many forces in action at the same time here, it's like herding cats.

I would start with a torque tab adjusting the trailing edge towards the Starboard because as I see it your trying to use only the trim to balance the steering instead of the external water pressure on the tab, hopefully then you can trim to neutral without porpoising.

Need to start thinking action/reaction (Newton).

 

[juicegoose]

So even with the seastar hydraulic steering( not powered hydraulics just normal) i could benefit from a tab? I was told it wouldnt help