Boat almost tipping over.

[daviddsims]

I just bought a used avanti 1985 17 feet ski boat with a 120 hp mercruiser motor and an 18 pitch stainless prop. My question is when i take off with the trim down and start going up the boat sometimes goes dangerously close to tipping over on one side. Maybe I am just not experinced enough or is this a problem with the boat? Any help would be appreciated. Thank you

 

[Boomyal]

Re: Boat almost tipping over.

does the motor have a fin bolted to the cavitation plate?

 

[daviddsims]

Re: Boat almost tipping over.

Right above the prop there is a small fin welded to something called a hydro stabilizer. I really dont know what a cavitation plate is.

 

[crazy charlie]

Re: Boat almost tipping over.

Sounds like you are putting the tabs down too far and does the boat sit level at rest or does it have a list to one side?? There should be skeg/fin over the prop and it should be relatively straight and not angled to one side.Also make sure you have your occupants situated evenly in the boat at all times.If there are two of you make sure that there is one on each side.Do the same with gear.Post back any results.Charlie

 

[DJ]

Re: Boat almost tipping over.

The cavitation plate is the long plate just above the propeller. It has a fin hanging down just behind, and above, the propeller.<br /><br />If there is a large fin bolted to, or welded on, to that plate. I would get rid of it. You do not need it with trim tabs.

 

[dajohnson53]

Re: Boat almost tipping over.

Daviddsims: do you have trim tabs? Some of these replies assume you do. Or are you just talking about the trim of the outdrive on your mercruiser?

 

[Boomyal]

Re: Boat almost tipping over.

daviddsims, post a picture of the stern and lower drive of your boat.

 

[daviddsims]

Re: Boat almost tipping over.

Not sure if i did the pic right as I have never added a pic online but no I do not have trim tabs just trim on the outdrive.

 

[daviddsims]

Re: Boat almost tipping over.

back of boat

 

[RotaryRacer]

Re: Boat almost tipping over.

You have the right idea with the picture but I still can't see it. Do you know if imageshack requires you to register and log-in before you can use them to view hosted pictures?

 

[daviddsims]

Re: Boat almost tipping over.

 

[daviddsims]

Re: Boat almost tipping over.

<br />Hope this helps.

 

[SS MAYFLOAT]

Re: Boat almost tipping over.

Looks to me those fins are mounted backwards.

 

[SS MAYFLOAT]

Re: Boat almost tipping over.

Yes, they are mounted wrong. The left one should be on the right and vice versa. The thin edge of the hydrofoil is to be towards the back or the boat. The thin edge could be flexing forcing your boat to lean. The thick leading edge should be pointed forwards.<br /><br />I wouldn't run your boat with them installed the way they are. It could be dangerous.

 

[daviddsims]

Re: Boat almost tipping over.

How can that be? It has arrows on the bottom that point forward and if you swap them it wouldnt be right.

 

[Maximerc]

Re: Boat almost tipping over.

Take them off ... I think they are installed correctly .. if you turn them around they will be pointing down,and thats not right. It may be that they are old and weak and flexing down if you need something on that order look at smart tabs.

 

[daviddsims]

Re: Boat almost tipping over.

I know that there are alot of threads on smart tabs but how hard are they to install and what would be my benefit as i just intertube and kneeboard? I just dont want the boat tipping over lol.

 

[JasonJ]

Re: Boat almost tipping over.

I have the same foil, they are mounted correctly. It looks like they are on wrong because of the angle they are being viewed in the lower pic. They do not sit horizontal like a regular foil, they angle upward to each side, so that they are theoretically mostly out of the water when at plane.<br /><br />You should work with your trimming technique before you start throwing parts at it. The fact that you are saying it sometimes does it tells me you are not utilizing your trim in a consistant manner. It makes a big difference. <br /><br />Once it comes on plane you need to trim out, or it will pull to one side (wich will make it feel like it is "tipping over"). Trimming out lessens the prop torques effect on the boat. You may also need to adjust the small fin above the prop, but try the trimming technique first. Trim tabs would eleviate the problem you are experiencing because the aft end ot the boat would be lifted from each side of the outdrive instead of centralized outdrive itself, but try experimenting first.

 

[SS MAYFLOAT]

Re: Boat almost tipping over.

Sorry about misleading you. (got called in to work right after I posted) I had ones on my outdrive that looked identical to them. The directions on them were the opposite. I didn't have any problems with them though. Good luck, Jason is correct about the trim. It isn't something that you can set a forget. Keeping weight balanced within your boat helps a bunch.

 

[Jdeagro]

Re: Boat almost tipping over.

Daviddsims;<br /><br />You need to understand the effect of the motor trim, and the hydrofoil on your boat. Without going into a long post here let me suggest that you send me your mailing address and I will send you a booklet of boat balance and performance no charge. Anyone else is welcome to have a copy also.<br /><br />You are trimming the motro down at take off and once on plane you need to bring it up, but this is not why you are "bow steering" the boat.<br /><br />The prop is lifting the stern as well as the Hydrofoil, and this pushes the bow down into the water. In doing so the bow is suseptable to radical steering in either direction because the knife edge of the "V" is deep in the water. Any shift in torque or load will make the boat lean and steer hard in that direction. <br /><br />Trimming the motor up removes some of the lift on the stern but the hydrofoil can not be adjusted. <br /><br />Trim Tabs and Smart Tabs are adjustable. Smart Tabs are automatic in this regard, and designed to be installed by the average consumer. Trim Tabs stabilize the boat because they are not lifting from the center but either side. <br /><br />IMHO hydrofoils are anything but stabilizers, unless mounted on each side of the boat on a twiin engine rig.