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Old 09 February 2008, 18:08   #1
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Excesive Transom Water Splashing

Hola...

Have a new Sea Rider Sib 360 powered by a Tohatsu 2 strokes 18 HP short tail, yesterday that was first testing the sib on very calm waters noticed that there was excessive water splashing at the transom & tube cone area.

This is an ideal family boat for 5, can handle well a 25 HP engine very smooth. I usually go boating with just 2, my copilot buddy and myself, that’s because we like to obtain the best speed on calm waters nearly going full throtle and to be extreme confortable with gear and enough space to move in.

Here is a precise data on the sibs configuration setup to reach a true technical verdict : See atached pics

Have secured the 6.5 Gal gas tank, the anchor, chain, extra ropes under the prows front bag by means of extra d’rings (will not move a bit) this gives me about 35 kilos on the prow to balance better the sib. (don’t like bumpy prows) Usually drive seated on the right tube with my left arm very extended but comfortable to stear, my buddy sits on the opposite tube in front of me, the trim angle was set at the second position near the transom (in trim) so to have the sibs bottom parallel with the cavitation plate.

Have measured the distance from the sibs bottom to the cavitation plate, is around 7-8 cm, the splash seems to come from the lower engine mount bracket, when speeding water strikes the bracket water is forced upwards the transom side and entering the sib. The engine manual specifies that the ideal distance from the any boats bottom to the cavitation plate must be only 25 to 50 mm. So I’m missing the ideal set up for 30 to 40 mm. At this position the anticavitation plate slightly is not parallel to the sibs bottom.

The water splashes lessens when the trim angle is set at position 3 (in trim, the engine has 6 holes) What I would like to know is:

Placing a doel fin or trim tabs will better this water fountain situation. Would not like for the moment to modify my transom height for the complexity of the transom, that is a has a mould like hard plastic protector that secures and water tights the upper transom’s marine play wood transom.

Tomorrow will make a early sea test with a third buda sitting on the front bench + a full gas tank to balance better the boat to see what happens. (trial & error basically) Other than the spalsh issue the boat is performing extremely well and maneourable.

Any advise, suggestions will be highly appreciated.

Happy Boating
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Old 09 February 2008, 19:14   #2
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have you tried it trimmed right in on the first hole . My honda 3.8 was best in that position . other owners have said the same , and your sib looks very similar .
My zodiac also used to spray some water back up the transom , I think it may be just something sibs do because of the soft floor creating an uneven water flow compared to a hard hull , that was my reason for it anyway and i never cured it .
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Old 09 February 2008, 19:52   #3
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My Quicksilver 3.1 with a suzuki 15hp doesn't do this.

You could prob rise the engine height a little just by putting a wooden block/rod under the engine on top of the transom.

If all else fails you could rig up some sort of aluminium shield to deflect the water away.

And talking of the 18hp - I just tried to buy one - no short shafts left in the UK and the longs are electric start remote steering!!!
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Old 10 February 2008, 03:54   #4
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Spray from behind

I have the same problem with my Zodiac Futura 11C with an inflatable floor and an 18hp Tohatsu. A boat that we use a tender for my sailing boat. I have tried moving the engine up on a wooden block which makes for a slight improvement but more cavitation but think the basic problem is the water flow from the Zodiac against the blunt front of leg on the Tohatsu.
This is the second time this has happened to me with a Zodiac - the last time was with a 15hp Evinrude on my Fastroller 3.20 which I struggled with for 10 years.
I think the answer may be to get a tube maker to extend the floor aft to reduce the gap between the outboard leg and the transom.
I find it bizarre that a boat manufacturer with this history and reputation gets this wrong for so long. In my case for 13 years. Gavin
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Old 10 February 2008, 07:33   #5
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Quote:
Originally Posted by ian parkes View Post
have you tried it trimmed right in on the first hole . My honda 3.8 was best in that position . other owners have said the same , and your sib looks very similar .
My zodiac also used to spray some water back up the transom , I think it may be just something sibs do because of the soft floor creating an uneven water flow compared to a hard hull , that was my reason for it anyway and i never cured it .
Hola Ian:

My 360 sib is a aluminum floor, has extra wide tubes and is inflated to the correct pressure (0.25 Bar) for rigidity. Has risen the engine a bit, will see the water performance latter. 18 HP short tail if fine with this sib lenght, can accept a 25 with no problem. Have trimed it in the first hole, the one near the transom, perform worst, tried the second, was better, the third seems to be nearly ok once on plain,

Had a Evinrude 15 HP short tail, find the engine clamps to be a bit longer, the clamps used to be secured in the middle of the engine plate, the Toh are just reaching the plate's upper border. This will make impossible to put a higher wooden block because the fastening clamps will be reaching the engine plate border and it has a large protuberance rim.

My old Zodiac 305 & Quicksilver 330 did not spray a single drop of water to the inside. Noticed that had different transom angles though and probably the Evi engine had a higher mounting lower bracket.

Thanks all for the imput, will see later under trial & error...
LocoZ
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Old 20 February 2008, 15:12   #6
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Quote:
Originally Posted by Locozodiac
My old Zodiac 305 & Quicksilver 330 did not spray a single drop of water to the inside...
Does the water actually come into the boat, does it just do a bit of a 'rooster' either side of the engine?

If it is the former, that sounds very wrong indeed.

If it is the latter - some boats just do that. My Ribcraft will do it at a particular throttle setting, as will my little tender (with a 4HP). I have always assumed that it is just a characteristic of a particular combination of engine/leg/prop and boat - and unless the performance of your boat is badly affected - or it does it all the time - then it will probably take up a lot of time and effort to eliminate something that might not make much difference.

IMHO, obviously...
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Old 20 February 2008, 15:28   #7
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I have a similar problem on my Rigiflex and 15hp short shaft Mariner. Trimming out doesnt do anything. Very weird as I used to use an identicle set-up which didnt.
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Old 21 February 2008, 09:19   #8
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[QUOTE] Does the water actually come into the boat, does it just do a bit of a 'rooster' either side of the engine?

If it is the former, that sounds very wrong indeed. If it is the latter - some boats just do that.
------------------------------------------------------------------------

Had a OMC 305 and a Quicksilver 330 but used with a Evinrude 15 HP 2 stroke engine with no water splash problems at all. In my particalar case water roosters (circles) the transom/tube area and tends to get in, have to put passengers and complete cargo to the bow to rise the engine and put the trim angle to a position (hole 3) that is not the correct to have a 90 angle ( hole 2) between sibs bottom/engine/cav plate while on plane.

This new 360 sib uses a Tohatsu 18 HP short tail engine which is a great combination weight/ratio, the manufacturer strongly recommends a height between 3 to 5 cm from the boat's bottom to the anticavitation plate, my sib has 7 cm exceeding by 2 the maximum distance. So will modify my 38 cm transom height to match my engine, that is fill in with fiberglass/epoxic resins the v transom shape to risen to 40 cm and make a straight transom, With the final height modification my anticavitation plate will be 4.5 cm inside Tohatsu recommended height measurements (3 to 5 cm from boat's botom)

The problem is a sib/transom height /engine leg issue that has to be corrected. This water splash tends to slow a bit the wot emgine/sib speed and don't plan to place triangle anti water splashers at both transom/tubes ends. Will need to rise the transom's front engine & rear mount plates accordingly to match the new 40 cm height. Will let you know what happened...

Happy Boating
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Old 21 February 2008, 09:31   #9
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Quote:
Originally Posted by Tim M View Post
I have a similar problem on my Rigiflex and 15hp short shaft Mariner. Trimming out doesnt do anything. Very weird as I used to use an identicle set-up which didnt.
If your Mariner 15 HP is recently manufactured like this pic it's a disguissed Tohatsu engine, it's the same size as the 10/15/18 models, all will splash or cavitate the same if not under the manufacturers specs, see if your anticavitation plate is between 3 to 5 cm from your boat's bottom.

Some Mercury/Mariner/Tohatsu/Nissan engines of this rated HP attached to small/medium sibs transoms will have the same problem. Have tried my Toh 18 HP 2 strokes on a 420 Sib transom, whick is some cm higher and don't have this water splash. So there might be a transom height/leg issue technical water problem with these brands if used un correctly.

What was your previous if so, identical set-up which didn't splash ?

Happy Boating
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Old 21 February 2008, 11:47   #10
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Could be that the motor is mounted too low. Excessive LU in the water will cause the rooster tails out to the sides of the motor.

The "cav plate even with the bottom of the hull" thing is a good starting point, but is not cast in stone. Many boats perform best with the cav plate a few inches higher than the bottom of the hull.

Something to think about, anyway. Takes a bit to correct, though. If you try it, make sure you seal up the bolt holes to prevent rot and other water intrusion problems.


jky
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