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When motoring at 5 knots stern sits...Normal?

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albert
Captain

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USA
262 Posts

Initially Posted - 04/19/2002 : 01:33:10

I'm using a standard shaft 18 HP Tohatsu 2stroke electric start. It was the only available outboard (I already owned it)when my long shaft Johnson 15hp stopped cooperating.

Once I have forward momentum (5knots) the stern sits and prop works fine. One problem is that this "sitting" causes my standard bilge through hull to submerge.

Do Long and Extra Long shaft motors do the same? My original Johnson 15 lasted about a week after I purchased the boat. I never had a chance to observe the bilge through hull. I'm planning a new engine purchase and was wondering if an extra long shaft causes the stern to "sit" so low that the bilge through hull is under water.

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 04/19/2002 : 01:46:23

18HP! What are you doing, pulling skiers?

Do you have the proper trim set on your motor? Are you overpowering the boat? How heavy is an 18hp motor? On my old boat, I had a Johnson 9.9 and if I gave it too much throttle the stern would sit and I would start to slow down. I can't remember, but how high up from the waterline is the bilge thru hull?

Don Lucier, Northstar
C25 SR/FK

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Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 04/19/2002 : 03:17:09

You have several factors to think about here. Engine trim / pitch would be the first thing I would check. Next I would have a look at weight distribution / where is the most junk stored and perhaps move some up under the V berth. Third is how clean the keel and bottom of your boat is. Once you get near max hull speed the boat will squat if you push hard with a motor.

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 04/19/2002 : 14:35:34

Albert,
The length of the shaft has no effect on the boats squatting, more than likely the adjustment of the shaft angle is what needs correcting
. Bringing the shaft closer to the transom will force the stern up.

Val on the hard DAGNABIT

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
I'm using a standard shaft 18 HP Tohatsu 2stroke electric start. It was the only available outboard (I already owned it)when my long shaft Johnson 15hp stopped cooperating.

Once I have forward momentum (5knots) the stern sits and prop works fine. One problem is that this "sitting" causes my standard bilge through hull to submerge.

Do Long and Extra Long shaft motors do the same? My original Johnson 15 lasted about a week after I purchased the boat. I never had a chance to observe the bilge through hull. I'm planning a new engine purchase and was wondering if an extra long shaft causes the stern to "sit" so low that the bilge through hull is under water.

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Val Bisagni

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 04/19/2002 : 14:40:08

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>Once I have forward momentum (5knots) the stern sits and prop works fine. One problem is that this "sitting" causes my standard bilge through hull to submerge. <hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

I just came back from the boat and the distance from the center of my bilge thru-hull to the bottom of my waterline stripe is 10". If your stern is squatting 10" while motoring then something definitely needs to be addressed(too much throttle, motor trim, load balancing, motor weight,...etc).

Don Lucier, Northstar
C25 SR/FK

Edited by - on

albert
Captain

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USA
262 Posts

Response Posted - 04/19/2002 : 18:41:00

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
18HP! What are you doing, pulling skiers?

Do you have the proper trim set on your motor? Are you overpowering the boat? How heavy is an 18hp motor? On my old boat, I had a Johnson 9.9 and if I gave it too much throttle the stern would sit and I would start to slow down. I can't remember, but how high up from the waterline is the bilge thru hull?

Don Lucier, Northstar
C25 SR/FK
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

No skiers. I tow a barge <img src=icon_smile_big.gif border=0 align=middle>! As i said it was available. I only use it at half throttle. It ways about 80lbs.

I was once told by an "expert" sailor that adjusting the trim on an outboard hung off of a displacement hull was a waste of time as the mass of the hull would determine how much the boat would 'sit'.

I just didn't think that Catalina would put a bilge thru hull below the waterline <img src=icon_smile_8ball.gif border=0 align=middle>.

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - albert on 04/19/2002 18:44:54

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 04/19/2002 : 19:30:18

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote> I was once told by an "expert" sailor that adjusting the trim on an outboard hung off of a displacement hull was a waste of time as the mass of the hull would determine how much the boat would 'sit'. <hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

If the outboard is trimmed up(canted back and up) and producing a roostertail, this is going to add weight to the stern from the force of the engine. I'm not a rocket scientist, but it only makes sense that the perceived weight of the motor has to increase the more the direction of force is pointing downward(towards the bottom) rather than straight ahead.

Don Lucier, Northstar
C25 SR/FK

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.