Lack of power - is it normal?

[soren]

Dear all

We are experiencing some problems with our Mb2/50s, since it barely gives us enough power to get out of and into the harbour. We have a "normal" 26 foot sailboat and a standard fixed-two-blade propellar.

The engine has normally (this is our first season) been able to drive us at about 3-4 knots in no-wind conditions, which I guess is OK, but not great. But yesterday we could barely enter the harbour, which caused some concern with the crew.

I would thus like to ask, 1) how much speed you get out of your engines and 2) if anyone has any idea of why the engine doesn't give us more power?

With best regards and many thanks for a great forum!

Soren

[Sarabande]

(26-07-2010 08:52 AM)soren Wrote:  Dear all

We are experiencing some problems with our Mb2/50s, since it barely gives us enough power to get out of and into the harbour. We have a "normal" 26 foot sailboat and a standard fixed-two-blade propellar.

The engine has normally (this is our first season) been able to drive us at about 3-4 knots in no-wind conditions, which I guess is OK, but not great. But yesterday we could barely enter the harbour, which caused some concern with the crew.

I would thus like to ask, 1) how much speed you get out of your engines and 2) if anyone has any idea of why the engine doesn't give us more power?

With best regards and many thanks for a great forum!

Soren

Are you sure you haven`t a "Dirty Bottom" or some weed around the prop?

[soren]

(26-07-2010 03:27 PM)Sarabande Wrote:  

(26-07-2010 08:52 AM)soren Wrote:  Dear all

We are experiencing some problems with our Mb2/50s, since it barely gives us enough power to get out of and into the harbour. We have a "normal" 26 foot sailboat and a standard fixed-two-blade propellar.

The engine has normally (this is our first season) been able to drive us at about 3-4 knots in no-wind conditions, which I guess is OK, but not great. But yesterday we could barely enter the harbour, which caused some concern with the crew.

I would thus like to ask, 1) how much speed you get out of your engines and 2) if anyone has any idea of why the engine doesn't give us more power?

With best regards and many thanks for a great forum!

Soren

Are you sure you haven`t a "Dirty Bottom" or some weed around the prop?

Thanks for your reply. Yes, I am quite sure that it is not because or dirt or weed. I checked it out while snorkling 2 weeks ago, and it looked fine. Do you have other ideas as to what might cause this lack of power?

With best regards,

Soren

[Sarabande]

I have an Achilles 24ft Fin keel yacht, the engine pushes her at 4knts comfortably. As you said it would push you along at 3 to 4 knots in calm water, I would expect the engine to struggle to push a 26Ft boat in Wind over tide conditions or against a current.
Presume there has been no fall in revs? Plug gap correct? fresh fuel? to confirm the engine is working correctly have a compression test done on the engine, this will tell you that (A) The engine is ok. (B) then the boat is underpowered

A more qualified Forumite should be along shortly to give advice

[John Smith]

(27-07-2010 08:12 AM)Sarabande Wrote:  I have an Achilles 24ft Fin keel yacht, the engine pushes her at 4knts comfortably. As you said it would push you along at 3 to 4 knots in calm water, I would expect the engine to struggle to push a 26Ft boat in Wind over tide conditions or against a current.
Presume there has been no fall in revs? Plug gap correct? fresh fuel? to confirm the engine is working correctly have a compression test done on the engine, this will tell you that (A) The engine is ok. (B) then the boat is underpowered

A more qualified Forumite should be along shortly to give advice

Hi.
This engine will drive my 23ft twin keel boat against a wind and a 3Kn tide with ease.
There are so many factors that could be taken into consideration concerning your problem that they are almost too numerous to list.
However, there are a few checks that you can do as a start.
1. How does the compression feel when pulling the starter cord? There should be a distinct "bump" as the pistons go over tdc.
2. Does the engine fire on both cylinders?
3. Does the engine rev freely on tickover, the book states 1200 rpm?
4. Is the oil in the oilpan clean? There may be water in the oil which gives the oil a milky colour. If so the main shaft seal is worn allowing water into the oil and increasing the pressure behind the pistons.
5. Check the timing marks.
6. Is the throttle movement restricted?
7. There may be fuel starvation to the carb'.

Anyway, let us know how you get on.
John Smith

[Trerophy]

(27-07-2010 08:12 AM)Sarabande Wrote:  I have an Achilles 24ft Fin keel yacht, the engine pushes her at 4knts comfortably. As you said it would push you along at 3 to 4 knots in calm water, I would expect the engine to struggle to push a 26Ft boat in Wind over tide conditions or against a current.
Presume there has been no fall in revs? Plug gap correct? fresh fuel? to confirm the engine is working correctly have a compression test done on the engine, this will tell you that (A) The engine is ok. (B) then the boat is underpowered

A more qualified Forumite should be along shortly to give advice

Seawolf 26 bilge keel weighs 3.5ton displaces 2.5ton will make 5 and a bit knots calm conditions with revs to spare but they make no more speed, the standard 2 blade prop must have to much pitch for a heavy boat. Generally cruise at 4 to 4.5 knots not much over half throttle tide/wind obviously makes a difference but is still a respectable turn of speed for 7.5hp.
Check your sheer pin normally loose drive totally but it may be the prop is tight enough to drive a bit.

[Ciao Bye]

Mirage 25 4000 pounds cruising max 5.3 knt.

Have you check the max rpm while running?

I have one connected all the time to the engine and run it a 75% of it's peak power to limit the fatigue.

I once had a similar problem and changed the plugs. I had a faulty one. Hope this can help you.

John
Quebec
Canada

[billyjmcd]

(28-07-2010 06:14 PM)Ciao Bye Wrote:  Mirage 25 4000 pounds cruising max 5.3 knt.

Have you check the max rpm while running?

I have one connected all the time to the engine and run it a 75% of it's peak power to limit the fatigue.

I once had a similar problem and changed the plugs. I had a faulty one. Hope this can help you.

John
Quebec
Canada

did the engine start to lack power going astern first and then start to loose power going ahead.i had a simular problem 1 changed the gear box back in the water after 15 min back to same prob.2 replaced the engine and saildrive putting the prop on i noticed something was not right i put the engine in gear and the prop would turn replaced the prop and everthing o.k. worth going under again and checking?

[Howard]

I have a 25 foot jaguar and it drives the boat at 6.5 kns with about 5.5kns into a force 5 / 6 you have a seroius lack of power or a very dirty prop & bottom. I am aware of boat speed situations down to 3 kns with just marine growth, this year from all reports has been rather worse than normal, Howard

If it starts ok then I would look under the boat first