Water spraying up from engine

[MarshMarlowe]

1997 C90 TLRV

My C90 kicks up a lot of spray in front of the engine when I run my boat at planing speed. Trimming out only helps a little. Some of that spray ends up coming back into the boat. I've been told that once upon a time, there was a "Spray Deflector" / "Splash Guard" (not sure of the proper term) that was mounted on the high thrust version of this engine that was much more substantial and kept that spray down.

My motor is mounted high enough that the spray deflector is not buried in the water and unable to do its job. The cav plate is where it needs to be in relation to the water. My hull has a pocket in the transom that sends spray up towards the engine, and that little spray deflector on the C90 is all but ineffective.

Here are some pictures to illustrate what I'm looking for-







Does anyone happen to know a part number I can drill/bolt on to my engine? They seem to be readily available for older OMC engines, but I can't find anything for Yamaha. If no part number, has anyone fabricated something like this?

[boscoe99]

Can you see the anti-ventilation plate when the boat is running at speed with the motor trimmed to the most efficient trim angle? From an efficiency stand point the plate should be riding on the surface of the water. Higher if the propeller does not ventilate.

Most Yams come from the boat builder or dealer mounted lower than is optimum.

Check out this video. Look at the plate at about one minute into the video. Might be just a tad high but there is little splash from the lower unit.

https://www.youtube.com/watch?v=15QnJHiwkBw

This one seems to be spot on at the end of the video.

https://www.youtube.com/watch?v=_Pb5cGHikwc

But to answer your question, Yamaha does not offer an add on anti splash plate.

[MarshMarlowe]

Can you see the anti-ventilation plate when the boat is running at speed with the motor trimmed to the most efficient trim angle? From an efficiency stand point the plate should be riding on the surface of the water. Higher if the propeller does not ventilate.

Most Yams come from the boat builder or dealer mounted lower than is optimum.

Check out this video. Look at the plate at about one minute into the video. Might be just a tad high but there is little splash from the lower unit.

https://www.youtube.com/watch?v=15QnJHiwkBw

This one seems to be spot on at the end of the video.

https://www.youtube.com/watch?v=_Pb5cGHikwc

But to answer your question, Yamaha does not offer an add on anti splash plate.

Yes, I can see the anti ventilation (cav) plate when running at planing speed with the engine trimmed. The motor is mounted at the 3rd hole down from the top. The factory had this engine mounted at the 2nd hole down. At the 3rd hole down where it is now, the engine is on the cusp of cavitating.

In the first video, the vee keel of the boat extends completely to the transom. My boat (Key West 1720) has a notch in the transom, and redirects spray up at the motor, exacerbating the spray issue.

If a spray deflector isn't available, then I might see about fabbing one from a dole fin.

[99yam40]

Did the spray get worse or better when you raised the motor?

[MarshMarlowe]

Did the spray get worse or better when you raised the motor?

I'm not sure. The engines always been mounted on the third hole since I've owned the boat. I've thought about lowering the engine to the 2nd hole, but the guys running this engine on their Key West 1720s have reported lower top end speed with the engine mounted at the 2nd hole (same prop). Do you think lowering the engine might help with the spray?

[99yam40]

I was just wondering if it made a difference.

Do the other guys running a boat just like yours,and set up the same way, have the spray problem?

Pockets tend to push water up at the motor and prop at speed so not sure how to correct it.
But a small loss of speed to get rid of the spray may be worth it if that helps

[MarshMarlowe]

I was just wondering if it made a difference.

Do the other guys running a boat just like yours,and set up the same way, have the spray problem?

Yes

172 sportsman yamaha 90 spraying water : Engines, Electronics, and Hydraulics


1720 motor too short? : Props and Performance

[99yam40]

If they never found a cure for that boat and motor set up, then you are on your own to find a cure.
If you do modify the fin and it works please post a pic of what you did here and on the other places to help others.

Something on motor or transom to deflect the spray may hep a lot of folks. I see spray on boats all the time out running

Have you pulled the tail off yet to see how that affects things?
Some props tend to lift the bow more than others , This may be the reason they put the tail/fin on to stop the porpoising.
I took the fin off my C40 16 SV Xpress and could not run without putting someone on the bow to stop the porpoising. So I put it back on

[SeaDawg3]

Marsh, I think it is just a characteristic of the yamaha 90. after reading about the subject I now know this is the norm with the small splash plate on the 90.

when I had the 2002 yam 90 mounted in the #2 hole on the SH 172 I really didn`t take much notice of the spray probably bc it didn`t grab my attention.

but when I raised my engine to the 3rd hole to get the AV plate in the correct height the first thing I noticed was the increase in splash back.

but ours seems to be just the opposite of yours. If I trim in, the spray is close to the boat and very wide. If I trim out for optimal running at cruising speeds that large wide pattern diminishes.

[boscoe99]

Marsh, I think it is just a characteristic of the yamaha 90. after reading about the subject I now know this is the norm with the small splash plate on the 90.

when I had the 2002 yam 90 mounted in the #2 hole on the SH 172 I really didn`t take much notice of the spray probably bc it didn`t grab my attention.

but when I raised my engine to the 3rd hole to get the AV plate in the correct height the first thing I noticed was the increase in splash back.

but ours seems to be just the opposite of yours. If I trim in, the spray is close to the boat and very wide. If I trim out for optimal running at cruising speeds that large wide pattern diminishes.

The 90 in the first video and the F100 (same gear case as a 90) in the second video don't appear to me to have an excessive amount of splash.

Are we not in agreement as to what excessive splash means?

[boscoe99]

Should be a fairly simple matter of fabricating a flat piece of aluminum into a horse shoe shape that can be riveted/welded/bonded to bottom of the upper casing. Maybe extended aft to the point that the forward lower unit attach bolts would secure it in place.

[SeaDawg3]

I can`t explain it, after speaking with boaters, some have it and some not. maybe the transom degree/angle plays apart, I don`t know, but I can say that there was def a visual difference, and wet difference going from the #2 position to the #3. Ours does not blow back into the boat unless there is a good wind. The Fan spray pattern is very wide at trimmed in positions and taller than the height of the stern... it does settle down when trimmed out and cruising 25-27mph.

[robert graham]

The C90 on my 1870 jon boat throws a good bit of spray at speed until I trim it up a bit....then just a normal amount.....the deadrise at the transom is 6 degrees, if that has anything to do with it. But none of the spray finds it's way into the back of the boat....

[boscoe99]

The C90 on my 1870 jon boat throws a good bit of spray at speed until I trim it up a bit....then just a normal amount.....the deadrise at the transom is 6 degrees, if that has anything to do with it. But none of the spray finds it's way into the back of the boat....

That is the part that I am not understanding. Spray yes. Spray that goes forward to the point that it can get into the boat, no.

[MarshMarlowe]

Should be a fairly simple matter of fabricating a flat piece of aluminum into a horse shoe shape that can be riveted/welded/bonded to bottom of the upper casing. Maybe extended aft to the point that the forward lower unit attach bolts would secure it in place.

Thanks for the tip. Seems like it'd be simple enough

Have you pulled the tail off yet to see how that affects things?

My motor doesn't have a whale tail fin, but I do have one in the garage that came from another engine.

Marsh, I think it is just a characteristic of the yamaha 90. after reading about the subject I now know this is the norm with the small splash plate on the 90.

when I had the 2002 yam 90 mounted in the #2 hole on the SH 172 I really didn`t take much notice of the spray probably bc it didn`t grab my attention.

but when I raised my engine to the 3rd hole to get the AV plate in the correct height the first thing I noticed was the increase in splash back.

but ours seems to be just the opposite of yours. If I trim in, the spray is close to the boat and very wide. If I trim out for optimal running at cruising speeds that large wide pattern diminishes.

Your post really makes me consider lowering the motor one hole. The motor seems to want to cavitate easily in a turn with the engine mounted at the 3rd hole. Interesting that raising the motor created more spray.

That is the part that I am not understanding. Spray yes. Spray that goes forward to the point that it can get into the boat, no.

I know it seems unlikely, but it's happening. I have a pair of storage boxes in the stern - battery box and livewell. Both the battery box and livewell end up with water in them at the end of a day on the water (the livewell gets water in it without turning on the pump). Other owners of this boat+engine combo have reported the same issue with spray getting into the boat. It may actually be spraying onto the side of the transom notch and flowing down into the boat. I know it's getting on the gunwale portion of the transom.

I've uploaded a video of how much spray the motor is kicking up when planing out. Trimming out helps, but the negative trim is unavoidable when throttling up to plane, and that's when the spray is getting into the boat

Sorry for the low quality. I'm not actually running the boat through a worm hole, my phone's video camera is not very good.

https://www.youtube.com/watch?v=_GDx...Q#action=share