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Hull tilt while cruising

am_dew

am_dew

Advanced Contributor
"Ever since switching from a L

"Ever since switching from a LH to a RH prop, my boat tilts to the port side while cruising with one adult on the port side (and me driving on the starboard side). Short of going back to the old prop (don't want to as it's a lower pitch and this one is perfect for the boat except this tilt issue), buying a LH prop, or remounting the gas tank to the starboard side of the transom, which is not an option for me, and there is no weight I can redistribute. My boat has old style "Step n Trim" trim plates on the transom (see pic below) which can be manually adjusted and I am wondering if adjusting one of them either up or down would help? If so, which one should I adjust and in which direction?
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Transom
 
"If listing to port, RH prop m

"If listing to port, RH prop makes it worse.
If Your tabs are adjustable, try to 'lift' stb tab. From what I see at the pick that one seems to be pressing down more than port. Alternativet 'lower' port tab. The more You lower the tabs, bow goes down, but easier planning and less top speed."
 
How do you swap from a LH to a

How do you swap from a LH to a RH prop dosnt the rotation of the propshaft determin which hand prop you use?
 
"Take off the rear cover on th

"Take off the rear cover on the drive, move vertical rod to the other side.
Can't be more simple."
 
"Thanks Morten. The pic is a l

"Thanks Morten. The pic is a little deceptive, but both tabs look equally adjusted to the eye. They are both angled pretty much in line with the bottom of the hull...very little, if any dip or raise when compared to the bottom of the hull at the tab's mount points. I will try lowering the port tab a little and raising the stb tab a little and see what happens."
 
"Also, I wanted to clarify wha

"Also, I wanted to clarify what I mean by lowering or raising the tabs. The vertical position of the tabs cannot be changed...they are secured to the transom with no adjustment points. However, what is adjustable is the angle of the tab in relation to the hull. Here is a closer view of a tab...the dark brown things are allen head screws which need to be loosened in order to adjust the angle.

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Tab
 
I'm familiar with the syst

I'm familiar with the system.
Another question:
It seems to be a non-high speed prop on the boat. What pitch are You running?
 
"Bob, I have "step N trim&

"Bob, I have "step N trim" tabs also. And I also have a list... to starboard when at high speed. I have been reluctant to mess with the trim tabs... intimidated by the obvious rust/corrosion on the steel allen head bolts screwed into the alloy tabs. If you figure out a good way to get the allen head bolts loose please post it. I have been worried that putting a lot of torque on the allen bolts might cause the tab to transom hardware to pull out of the transom. That would be really bad news!!

Thanks!"
 
"Morten, that prop is a Volvo

"Morten, that prop is a Volvo OEM RH 14x19...works perfectly on the boat except for the list.

Matt, yea I am also concerned about loosening those allen head screws...the last thing I want it for those tabs to pull out of the transom! I plan on soaking them with Liquid Wrench before I try to loosen them."
 
"Matt, what prop are you runni

"Matt, what prop are you running? If a 14x19 RH in great shape, Maybe we could trade my RH for your LH?!"
 
"So sorry guys...I checked my

"So sorry guys...I checked my records and the above pic was taken *before* I switched to the 14x19 I installed a few weeks after the pic was taken. The prop in this pic is a 14x17. And since I switched the position of the rod under the cover, I know it's opposite of the one you see in the pic.
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I just re-read my last post...

I just re-read my last post...confusing as all heck! Bottom line is that the prop in the pic is a LH 14x17 but the prop I have on the boat now is a RH 14x19
 
"Higher pitched props tend to

"Higher pitched props tend to "twist" the hull more than lower pitch props. Its just a matter of physics. Prop goes round and round, some force goes backwards(boat moves forward), some sideways (boat lists). The only way to totally avoid that effect is to change boat to a paddlewheel :) Some hulls exhibit the effect more than others, smaller lighter boats more so.
When a marine architect designs a boat, they take that into effect, soooo, they use a LH rotation prop and then locate the helm on starboard so that the skipper's weight counterbalances the props torquing of the hull.
When you changed from a LH to a RH prop, your weight at the helm, instead of tending to counerbalance the hull twisting torque of the prop, added to it. You MAY be able to correct the effect with the trip tab, HOWEVER, that adjustment will increase drag on the hull. Your best bet... go back to a LH prop."
 
"Robert, thanks for your analy

"Robert, thanks for your analysis. I have come to the conclusion that, as you said, going back to a LH prop is my best bet. I bought this RH one when I was shopping around for a 14x19 and despite it being a RH, I could not pass up the deal (USD$40 shipped, OEM, and in great shape). Now I just need to find a similar deal on a LH 14x19.

I may try adjusting the trim tabs slightly to see if that helps without increasing hull drag to badly. It's either that or get a slimmer girlfriend to sit on the port side!
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"Gentlemen, since you asked,

"Gentlemen, since you asked, I am running a 14X17 prop on my VP 170/270. I believe it is a LH but I am not at the boat to confirm. I have 2 identical (one for spare) and they seem to be the correct pitch. Boat does (or did until today) about 25 mph at 4200 rpm according to the old instruments in the dash. That's lightly loaded and WOT. @ the throttle handle. Linkage @ carbs may be adjustable for more. Ran good until a couple hours ago when cruising at 2200 RPM just off plane it started to knock somewhere in the motor. Possible dropped valve, stuck lifter, spun bearing, or broken valve spring type noise as far as I can tell from outside. I have not pulled the valve cover to investigate it yet. Motor ran well enough to get back to ramp and load but is obviously running on less than 6 cylinders and does not want to idle. When it started making noise I reved it up for a second or two to see if the sound changed any and it got quieter at higher RPMs but still there. Worst seemed to be when it was coming back down from 3000 to just above idle (in gear of coarse--never take it over 2200 or so w/o a load). Anyway, sorry for the long post and off topic for Bob's trim tabs !! I will start a new string after I have enough beer to steel the nerves go pull it apart and have a look see.

Matt"
 
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