Raising an outboard?

[MikDee]

Re: Raising an outboard?

It's hard to see clearly because of the shadows in the Pics, but in the 1st one it looks like your cavitation plate is too low (below the bottom) of the boat, this would cause the roosters. If your motor is held on by clamps, (not bolted) I've seen high speed water pressure push up, and lift the engine right off the boat! run a straightedge from the bottom of the boat to the cav plate, and try to get the cav plate even with, or slightly above the bottom of the boat. Also, the motor angle must be paralell with the hull before you do this, (besides that is the best setting to start out with).

 

[Bass Tracker TX17]

Re: Raising an outboard?

So what you are saying is you think it is the design of the boat?!?!?

The back of the boats last 6 or 8" curves back down. If you were to take the sender off and secure it out of the water and run the boat then you could see if you had to even rooster tails on both ends of the boat.

I remember a long time ago my uncle had a boat that had the looks of a old Plymouth with high fins in the back. The boat had rooster tails from the back of the boat on both sides. Looked cool

There are 3 diff rooster tails it seems on this boat and members are giving you info on all of them.

I believe your major concern is the sender that CATransplant and Jack Daniels mentioned.

 

[Andy in NY]

Re: Raising an outboard?

Okay, I'll test it without the transducer.

 

[MikDee]

Re: Raising an outboard?

Taking a 2nd look, I'd say definitely it is water pressure pushing up against your cavitation plate at speed, causing the rooster tails. It's actually trying to lift the back end of your boat. It may look cool, but the boat is not running efficiently this way, you need to raise your motor like I said.

 

[Andy in NY]

Re: Raising an outboard?

Taking a 2nd look, I'd say definitely it is water pressure pushing up against your cavitation plate at speed, causing the rooster tails. It's actually trying to lift the back end of your boat. It may look cool, but the boat is not running efficiently this way, you need to raise your motor like I said.

So how exactly do I raise the motor?

 

[stevewolverton]

Re: Raising an outboard?

So how exactly do I raise the motor?

Jackplate.

This is the one I use. Simple, easy to install. http://www.iboats.com/T_H_Marine_Hi...13823715--**********.627105979--view_id.40130

 

[Andy in NY]

Re: Raising an outboard?

Okay, I started with using some plastic shims to raise the motor about 1/2 in at this point. I'm going to water test saturday, i'll let you know what I find. Also, I am going to raise the transducer up a bit too.

 

[Andy in NY]

Re: Raising an outboard?

Okay, here are the results. I raised the motor about a 1/2 inch, and it seemed to make it worse. I got rooster tails at a lower speed, and at WOT they were bigger than before. Also, the boat seemed a bit more sluggish than before.

Opinions?

 

[NSBCraig]

Re: Raising an outboard?

So where is your plate at compared to the bottom ?

 

[MikDee]

Re: Raising an outboard?

Okay, here are the results. I raised the motor about a 1/2 inch, and it seemed to make it worse. I got rooster tails at a lower speed, and at WOT they were bigger than before. Also, the boat seemed a bit more sluggish than before.

Opinions?

I don't know why it would be worse raising the motor? but, randomly moving the motor up 1/2" is not gonna make much of a difference. It's hard to tell from your side Pic. just where the cavitation plate on the motor is?
A better Pic. might help. I usually take a straight edge off the bottom of the boat at the keel, and adjust the tilt on the motor till it's paralell (your best setting to start with) then check to see if the motor needs to go up, or down, to make the cav. plate flush with the bottom, or up to at least 1" above it, again that is also your best setting to start with. Simply, the law of physics, has determined that the less lower unit in the water, the less drag.

 

[Andy in NY]

Re: Raising an outboard?

So where is your plate at compared to the bottom ?

This pic, for some reason it looks lower than it is, maybe the angle i took the pic?

I don't know why it would be worse raising the motor? but, randomly moving the motor up 1/2" is not gonna make much of a difference. It's hard to tell from your side Pic. just where the cavitation plate on the motor is?
A better Pic. might help. I usually take a straight edge off the bottom of the boat at the keel, and adjust the tilt on the motor till it's paralell (your best setting to start with) then check to see if the motor needs to go up, or down, to make the cav. plate flush with the bottom, or up to at least 1" above it, again that is also your best setting to start with. Simply, the law of physics, has determined that the less lower unit in the water, the less drag.

I'll try taking another pic with a straight edge tonight.

 

[NSBCraig]

Re: Raising an outboard?

Yeah it's real hard to tell in those pics where it's at.

Don't worry so much about getting a pic and posting it, just check it and let us know where your at so we can try to work it out.

You should be trying to get it just where mikdee said even or slightly above flush and level and then you can start dialing in from there.

 

[Andy in NY]

Re: Raising an outboard?

Now, I just want to make sure I am on the same page as you guys. The AV plate is the lower, larger plate just above the prop, correct?


Also, is it possible it is the hook eyes on the back are what are causing the rooster tails???

and, maybe i should ask thius in the prop section, but while you are here... what size prop should i be running? how do i find out what i have?

 

[MikDee]

Re: Raising an outboard?

The cavitation plate, is the large one above the prop, that's the one we're concerned with. The hook eyes? you mean the ones 1/2 way up the transom that usually your trailer straps are attached to? No Way! they're not even near the water! I think what's happening, is the boat bottom is a vee, and the cav. plate is flat, the water flowing quickly under your hull, is hitting the top of the plate, and shooting up, and to the sides. This is normal on most boats, but can get exaggerated if your lower unit is too long, or too deep. It's a worst case scenario with a long shaft motor (20"), on a transom designed for a short shaft motor (15"), that is not the case here as your transom, & lower unit appear to be a good match.

To match a prop, you need to know 1) What the WideOpenThrottle (WOT) RPM range for your particular motor is? 2) The RPM it hits now at WOT, and 3) The pitch number on the prop you're using now