TWO cavitation plate questions - trim tab and hydrofoil

[JoeMan]

My Merc 60 outboard is missing the trim tab (that's what I believe it's called), the little fin above the prop on the bottom of the cavitation plate. My understanding of the fin is that since the prop spins in one direction causing the motor to pull to one side, this little fin counteracts that pull while the boat is in motion, and also assists in low (no-wake) speed steering. Well, mine is missing. I was told by a well intentioned boater that with a boat as small as mine (16 foot aluminum runabout) that I could buy either a replacement fin for it, or a 'plug' which basically fits in there and makes the bottom of the plate flat instead of having the fin. Suggestion there? I am inclined to just get a new fin.
Secondly. I also have a hydrofoil on, and the nut ends of the bolts come through the bottom side of the plate. Should these bolts be turned upside down so that the water pressure from the prop is only pushing against round bolt heads instead of the nut and bolt ends?

 

[JoeMan]

Re: TWO cavitation plate questions - trim tab and hydrofoil

Hi guys, I've since learned that the Trim Tab is also called the Anode, and is very necessary for the lower unit...and only costs 10 bucks nearby. So the only thing I need to know is how much drag the nut and bolt is putting on the water flow under the hydro foil unit. THANKS.

 

[alana]

Re: TWO cavitation plate questions - trim tab and hydrofoil

years ago out of interest i tried the bolts bolts bothways and found no differance.but i did find that foils put more strain on the engine mountings than they are meant to have so shortening their life " heres a chance for the foil makers to shout"

 

[JoeMan]

Re: TWO cavitation plate questions - trim tab and hydrofoil

Thanks Alana. I look forward to more insight as well.

Here is my situation. This is my first boat, a 16 foot aluminum runabout from the 60's. Running the max size engine, a 60 hp (Merc, 1995). So, I have nothing to compare with. I'm thinking of removing the hydrofoil due to the 'drag' others tell me they cause, (in addition to the benefit of perhaps helping me plane) but I have NO clue really whether it's helping my boat or not. My guess is that a 60 set at the right trim should make this thing plane out just fine with or without it. Light weight boat. Thoughts?

 

[Silvertip]

Re: TWO cavitation plate questions - trim tab and hydrofoil

Go to Nauticus.com and read the article about the effects of a hydrofoil. I have used them in the past and eventually remove them. There are certain dynamics associated with foils (drag is only one) that in some severe cases can help a little but generally paying attention to engine height, boat loading (balance), prop selection, and trim settings results in a boat performing at is optimum. If additional help is needed, look to Smart Tabs especially if you have a stern heavy boat.

 

[alana]

Re: TWO cavitation plate questions - trim tab and hydrofoil

i agree with SILVERTIP

 

[JoeMan]

Re: TWO cavitation plate questions - trim tab and hydrofoil

Thanks Silvertip, in fact I'll also be trying a steeper pitch prop as well. Once I have my zinc anode on and try with a different prop or 2, I just may end up going without the Stingray foil at all. I do power trim the motor just slightly to help with plane as well. Thanks for the referral to Nauticus as well.