water deflecting off outboard and spraying over back sides of boat

[neversinksmith]

it didn't do this when I had my 85 merc 50hp on there. I 'upgraded' to a 73 merc 85hp and now this splashing is happening. I noticed that on the 50hp the leading edge of the lower mid section is shaped to cut through the water but on the old 85hp its pretty ugly as far as hydrodynamics. I cant tilt the outboard up any further or I get that bouncing effect at higher speeds. any suggestions? thanks

 

[Frank Acampora]

Simple: The engine is sitting too low on the transom. Raise the engine until the anti-ventilation plate is even with the hull bottom.

 

[Sea Rider]

Post a good quality large size pic showing your lower leg sideways as to check lower leg plates. OB's lower leg sizes and shapes vary among manufactures including same brand sizes. Many boaters have the wrong perception that's just a matter to sit any given engine on any given boat's transom and voil?. You are a clear example of "aint so"

Happy Boating

 

[neversinksmith]

cavitation plate is even w bot of boat

 

[Frank Acampora]

Because of a given hull's attitude in the water at speed, the water will tend to "rise" as it leaves the transom. try raising the engine about an inch and see what happens.

 

[neversinksmith]

ill give that a try. thanks

 

[Sea Rider]

Never..

That lower leg has a odd shape typical of old OB's.



If your engine has a sharp edge shape between WDP & AVP, raise engine with shims accordingly till water <<< flow skims right under WDP. For that to happen will need to know visually at which lower leg height is water flow passing by so to shim height right, could pull you head sideways out transom, have a second boat follow you next to your transom, use a go-pro camera installed on transom facing downwards. Engine must be trimmed at 90? and deck weight evenly distributed while at plane, rear large intakes between both plates should ride water submerged.

Happy Boating

 

[neversinksmith]

Never..

That lower leg has a odd shape typical of old OB's.



If your engine has a sharp edge shape between WDP & AVP, raise engine with shims accordingly till water <<< flow skims right under WDP. For that to happen will need to know visually at which lower leg height is water flow passing by so to shim height right, could pull you head sideways out transom, have a second boat follow you next to your transom, use a go-pro camera installed on transom facing downwards. Engine must be trimmed at 90? and deck weight evenly distributed while at plane, rear large intakes between both plates should ride water submerged.

Happy Boating

90* to water when at plane. or parallel to transom? (wdp?, avp?)

 

[bonz_d]

I find this very interesting as I too am facing the same issue w/o much success.

 

[Sea Rider]

If with manual trim, trim engine at 90? when boat is floating or trim engine if counting with power trim once riding on plane. Need boat's hull to plane parallel to water level, therefor will have both WDP & AVP riding parallel to water level too. The distance of both plates is very narrow compared to now a days new OB's, so dialing best leg height must be very precise.

Happy Boating

 

[neversinksmith]

I find this very interesting as I too am facing the same issue w/o much success.

what have you tried? whats worked what hasn't?

 

[bonz_d]

As of yet, nothing. Here is my thread and where it's at ATM.

http://forums.iboats.com/forum/boat...ding-and-hull-repair/10009676-jack-plate-help

 

[JimS123]

If I see the picture correctly, the motor has a hydrofoil on it. If that is the case, the height adjustment likely needs to be different that if it weren't there.

Definately, raise it.

 

[neversinksmith]

it still splashed water up when I removed hydrofoils. I just hate to keep drilling experimental holes in my boat moving the motor around. im at the lowest 'tilt' adjustment as of now. if I go up to the second hole from the transom, the boat bobs up and down in smooth water w/ two people in it as if im tilted up too high.

 

[JimS123]

That's a round bottom boat, not a deep-V. The 85 motor might be too heavy for the boat. Go back to the 50. What is the boat rated for? The second hole should be good for most any rig unless there is something wrong or mismatched.

 

[oldboat1]

^^might be right. too much weight. In your case, though, dropping the leg to about the level of that second plate (AV plate about an inch below bottom of the hull, guessing from pic), you might have more trim adjustment available without porpoising. Sage advice is usually to raise it, so might be counterintuitive....

(edit: mounting height issues aside, transom angle might be a factor. thinking matching the motor trim angle with the transom angle might be a better starting point, then adjusting trim angle for performance. Depending on your hull, that starting trim angle might be the optimum operating angle too. Also not orthodoxy, as outboards are typically mounted with the AV plate on the same plane as the boat bottom, regardless of or in spite of transom angle -- older Whalers, for example. I've sometimes found on my old hulls that hull characteristics, loading/balance, etc. can change that -- maybe motor weight too, in your case. )