27 Sailfish Cavitation Issue

Richard1572

Richard1572

GreatGrady Captain
Joined
Apr 26, 2008
Messages
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Location
Homestead, FL
Model
Sailfish
I purchased a 1996 27 Sailfish with 2004 Honda 225s. After taking it out a few times I’ve noticed that the Starboard engine seems to have a cavitation issue. The engine is constantly changing RPMs when on plane as if the prop isn’t biting. The port engine does not seem to have an issue. I measured and the engine’s cavitation plate is about 1 inch above the bottom of the hull (directly in front of the engine, not the keel). Looking more closely it looks like the previous owner had mounted the engine at several different heights trying to correct the problem. The port engine which does not have the issue is mounted at the exact some height. Both engines have the same Honda propeller (different rotation). Any suggestions or thoughts? I also noticed that there is a large through hull transducer on the starboard side. It is not directly in line with the engine, but could it make a bubble trail large enough that it ventilates the propeller?

Thanks for your assistance.
 
Sounds like you've already diagnosed your problem. You didn't say how far to the port or starboard the transducer centerline is from the motor centerline, or how wide and deep the transducer is - but you can almost bet it's the culprit.
 
gerrys said:
Sounds like you've already diagnosed your problem. You didn't say how far to the port or starboard the transducer centerline is from the motor centerline, or how wide and deep the transducer is - but you can almost bet it's the culprit.
Click to expand...

ditto

Airmar does make flush mounted transdeucers (600W and 1000W) which from the way things look will solve the problem. Some transeucers have a fairing the size larger than many shoes.
 
I wasn't sure if that was possible. Sounds like it is. The transducer is a Airmar b258 1 KW ceramic transducer. I hate to just toss it. Airmar makes a fairing block. Any chance that will reduce the bubble trail and help the situation?
 
Are both engines trimmed the same? Don't trust the gauge.

Set your trim the way you normally do, then dock the boat where you can walk away and see the beam at a distance, are both engines the same trim ?

And are they level with the water?

If not, level them to eachother and to the water, and go out for a ride, see what happens.

Over trimming can lead to cavitation, and only one engine may cavitate.
 
Is the 258 mounted without a fairing block? If so, exactly how is it mounted?
Adding the fairing block (assuming there's none there now) will only enlarge the profile and probably make the problem worse.

As Grog said, a flat mount transducer should resolve the issue. I'm not familiar with the sailfish, but the Marlin has two transducer flats moulded in the hull to mount transducers out of harms way. ??? sailfish???
 
There was some issues at my marina when they repowered a 28' HydraSport WA with twin suzuki's...... they ended up swapping lower units (changing counter rotating side) and that did the trick..... not sure if it is applicable here.
What does Honda recommend for center spacing?
Tim
 
i have a large 1kw airmar transducer mounted on the keel line in between my 2 x 200hpdi's and approx . 1 mtre forward. It has been mounted with and without the high speed fairing block with no probs either way. however if your transducer is closer to the starboard side and further to the rear ie. closer to the mtr. then it is certainly possible it is a likely cause.
 
richard1572 said:
I wasn't sure if that was possible. Sounds like it is. The transducer is a Airmar b258 1 KW ceramic transducer. I hate to just toss it. Airmar makes a fairing block. Any chance that will reduce the bubble trail and help the situation?
Click to expand...

I havd to agree that is probably the problem. Can you post a picture of the ducer installation?

If it is the problem, you always have to option of selling it on the classifieds here or on another forum, and putting the money toward a 1K flush-mount, or if you are able, you could remove the ducer, fiberglass the hole, and mount that ducer in the hull, by building a tank to set it in, then filling the tank box with pink anti-freeze or mineral spirits. It will work.
 
Thanks All,

I just purchased a flush mount tilted angle Airmar and will install it next weekend. I'll let you know if it worked. If anyone is interested I'm going to sell the old one.
 
Before you go changing anything with the transducer, motor height, etc., pull that prop to make sure you don't have a spun hub.
 
Good idea, I will remove the prop and check it now, but I doubt it because I don't notice the slippage until after I get on plane. I would think that if it was a spun prop the slipping would be worst when under full throttle and trying to get on plane.
 
Fixed!

It's been a long time, but thought I would post an update. I replaced the transducer with a flush mount unit. The cavitation problem has completely gone away. In addition the WOT on the engine without the cavitation issue increased by about 300 - 400 RPM, I guess because the other engine is pushing harder and top end increased by 7+ MPH. Amazing!
 
richard1572 said:
but could it make a bubble trail large enough that it ventilates the propeller?
Thanks for your assistance.
Click to expand...

It certainly could, and almost definitely is in this case.

I have posted in the past re the prop slip problem we had with a single engine on our Islander, due to the two scoop injectors (raw water washdown and livewell) mounted either side of the centerline and forward of the transom.

It doesn't take much of an "irregularity" in the bottom to cause turbulent flow and allow dissolved air to form bubbles.

Props don't like to bite in aerated (bubbly) water.

Brian
 
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