20hp prop or engine problem?

[mjbf15]

Re: 20hp prop or engine problem?

I took her out today and tried placing a 1x2 between the motor and transom and also played with the tilt pin. There was much improvement in performance. However, there still wasn't the speed I had hoped for....in water 3' or deeper. In 1-2' the boat was great! It got up on plane and really scooted along. I'm not a hydro mechanical engineer, so I really couldn't explain the phenomena. Can anyone shed light on this!

 

[mjbf15]

Re: 20hp prop or engine problem?

I was thinking that maybe there is some sort of "ground effect" going on in the shallow water just like an airplane only a few feet off the ground. The prop would also cavitate easily when I turned even slightly once on plane. I'm thinking of building a little jack plate for it to lift the motor out a couple more inches. Also would a hydrofoil help?

 

[tashasdaddy]

Re: 20hp prop or engine problem?

mjbf 15, email me these measurements. transom 16 1/2 inches, motor bracket to cav. plate 19". i think he should move motor up 2 to 2 1/2 inches. use a 1/4" mounting plate inside and out. to provide strength.. Ok, lets hear from all. come on guys, i want some feedback on my idea.

 

[tashasdaddy]

Re: 20hp prop or engine problem?

ok guys, what do you think of my idea? cheap shot to move this up.

 

[OBJ]

Re: 20hp prop or engine problem?

No cheap shot tash....boatwad takes cheap shots...... (probably shouldn't have posted that)<br /><br />Anyways....anything to get the cav plate up into the ball park.<br /><br />EDIT: Took another look at the pics....Matt would definitly need a riser on the transom to get the engine up. But we do have to remember that the water intake is on the tab hanging from the anti-cav plate. Might be a water starvation problem if we get it too high.....

 

[Paul Moir]

Re: 20hp prop or engine problem?

LOL at OBJ's cheap shot comment. What a horses arse that guy was! <br /><br />I hate to get the diagnosis off track, but what about checking for a blown prop hub? I know it doesn't sound *exactly* like it, but it's not all that different either. Or am I missing something?

 

[OBJ]

Re: 20hp prop or engine problem?

Dang Paul....you could be on to something here. I just re-read Matts original post....could be the hub is blown out. Maybe a direct question to Matt:<br /><br />Matt...does the engine rpm's seem to rise without the boat going any faster??

 

[mjbf15]

Re: 20hp prop or engine problem?

No, the rpms are steady, sounds slightly "bogged" down. I don't think it's a blown hub, but what are the indications if it is? However, like I said earlier the boat does great in shallow water, but then bogs down again in water approaching 3-4'. Does this mean anything to anyone.

 

[Paul Moir]

Re: 20hp prop or engine problem?

No, that doesn't sound like a blown hub. The symptoms of that are the RPMS rise up very high but the boat goes slow. Some people describe it as "popping out of gear".<br /><br />It sure sounds like a boat/setup problem. How does the hull bottom look? Any signs of it being bent inwards or outwards, or is it perfectly straight?

 

[mjbf15]

Re: 20hp prop or engine problem?

The hull is pretty straight.

 

[mjbf15]

Re: 20hp prop or engine problem?

Tashasdaddy emailed me a plan for a transom riser made of aluminum. I'm going to test run run with a 2x12 and some clamps. If there is improvement I think I'll just bolt the 2x12 to the transom at the correct height. Riser out of Al when my better half gets a job...