The right size prop?

Simon Neal · Joined: 17 Aug 2007 Posts: 1

Hi

I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
stroke engine. When I first bought the boat I had a new prop fitted
(Surveyor said it had leached or something). I let the yard I bought the
boat from do it. Didn't know enough about anything at the time. (still
don't!)

I have never had good performance from the engine. Despite a complete strip
down and re-build with new bearings seals etc. etc.and spot on timing under
load - set by timong gun. I make max 2 to 3 Knots and it always sounds quite
laboured and flat when under load, although it is perky and responsive out
of gear.

I was reading the engine spec the other day. It rates the engine as 10hp at
1650 rpm. I put a timing gun on it the other day. At full throttle under
load I never get above 800 rpm.

So is it possible that the yard put the wrong size prop on? How do I find
out what size prop I have at the moment. I have a bit of software to
recomend the correct size.

comments and speculation most welcome

Simon

Archived from group: uk>rec>boats>motor

Alec · Joined: 17 Aug 2007 Posts: 7

Hi Simon

Assuming that the engine is OK then either the prop is the wrong size or the
gearbox is the wrong ratio.

First check the gearbox ratio. (is there a gearbox?)

Some gearboxes have very different ratios in forward and reverse, does the
gear lever still work in the same direction as before , if not the new
propeller may be wrong handed.

To check the size of the prop you must have the boat out of the water, most
props are marked with the size on the boss (you may have to remove the nut).
Where is the old prop?

Assuming all above is OK then it sounds like the prop is too large. A
specialist may be able to modify it for you. They will also be able to
measure it for you.

If the old prop leached this means it dezincified, check your anode system
or it will happen again.

Alec

"Simon Neal" wrote in message$3mm$1$8300dec7@news.demon.co.uk...
> Hi
>
> I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
> stroke engine. When I first bought the boat I had a new prop fitted
> (Surveyor said it had leached or something). I let the yard I bought the
> boat from do it. Didn't know enough about anything at the time. (still
> don't!)
>
> I have never had good performance from the engine. Despite a complete
strip
> down and re-build with new bearings seals etc. etc.and spot on timing
under
> load - set by timong gun. I make max 2 to 3 Knots and it always sounds
quite
> laboured and flat when under load, although it is perky and responsive out
> of gear.
>
> I was reading the engine spec the other day. It rates the engine as 10hp
at
> 1650 rpm. I put a timing gun on it the other day. At full throttle under
> load I never get above 800 rpm.
>
> So is it possible that the yard put the wrong size prop on? How do I find
> out what size prop I have at the moment. I have a bit of software to
> recomend the correct size.
>
> comments and speculation most welcome
>
> Simon
>
>

---
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Checked by AVG anti-virus system (http://www.grisoft.com).
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Dave · Joined: 17 Aug 2007 Posts: 27

Simon

Try this site for info about props they may be able to help you
http://www.steeldevelopments.co.uk/

Regards

Dave

"Alec" wrote in message $paa$1@newsg1.svr.pol.co.uk...
> Hi Simon
>
> Assuming that the engine is OK then either the prop is the wrong size or
> the
> gearbox is the wrong ratio.
>
> First check the gearbox ratio. (is there a gearbox?)
>
> Some gearboxes have very different ratios in forward and reverse, does the
> gear lever still work in the same direction as before , if not the new
> propeller may be wrong handed.
>
> To check the size of the prop you must have the boat out of the water,
> most
> props are marked with the size on the boss (you may have to remove the
> nut).
> Where is the old prop?
>
> Assuming all above is OK then it sounds like the prop is too large. A
> specialist may be able to modify it for you. They will also be able to
> measure it for you.
>
> If the old prop leached this means it dezincified, check your anode system
> or it will happen again.
>
> Alec
>
>
> "Simon Neal" wrote in message
> $3mm$1$8300dec7@news.demon.co.uk...
>> Hi
>>
>> I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
>> stroke engine. When I first bought the boat I had a new prop fitted
>> (Surveyor said it had leached or something). I let the yard I bought the
>> boat from do it. Didn't know enough about anything at the time. (still
>> don't!)
>>
>> I have never had good performance from the engine. Despite a complete
> strip
>> down and re-build with new bearings seals etc. etc.and spot on timing
> under
>> load - set by timong gun. I make max 2 to 3 Knots and it always sounds
> quite
>> laboured and flat when under load, although it is perky and responsive
>> out
>> of gear.
>>
>> I was reading the engine spec the other day. It rates the engine as 10hp
> at
>> 1650 rpm. I put a timing gun on it the other day. At full throttle under
>> load I never get above 800 rpm.
>>
>> So is it possible that the yard put the wrong size prop on? How do I find
>> out what size prop I have at the moment. I have a bit of software to
>> recomend the correct size.
>>
>> comments and speculation most welcome
>>
>> Simon
>>
>>
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.752 / Virus Database: 503 - Release Date: 03/09/2004
>
>

Paul E. Bennett · Joined: 17 Aug 2007 Posts: 14

Simon Neal wrote:

> Hi
>
> I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
> stroke engine. When I first bought the boat I had a new prop fitted
> (Surveyor said it had leached or something). I let the yard I bought the
> boat from do it. Didn't know enough about anything at the time. (still
> don't!)
>
> I have never had good performance from the engine. Despite a complete
> strip down and re-build with new bearings seals etc. etc.and spot on
> timing under load - set by timong gun. I make max 2 to 3 Knots and it
> always sounds quite laboured and flat when under load, although it is
> perky and responsive out of gear.
>
> I was reading the engine spec the other day. It rates the engine as 10hp
> at 1650 rpm. I put a timing gun on it the other day. At full throttle
> under load I never get above 800 rpm.
>
> So is it possible that the yard put the wrong size prop on? How do I find
> out what size prop I have at the moment. I have a bit of software to
> recomend the correct size.
>
> comments and speculation most welcome
>
> Simon

Take a look at http://www.piranha.com/. There is a few pages that provide a
sort of tutorial to help you discover the right size of propellor for your
application.

--
********************************************************************
Paul E. Bennett ....................
Forth based HIDECS Consultancy .....
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

James · Joined: 17 Aug 2007 Posts: 5

"Paul E. Bennett" wrote in message$r0s$1$8300dec7@news.demon.co.uk...
> Simon Neal wrote:
>
> > Hi
> >
> > I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
> > stroke engine. When I first bought the boat I had a new prop fitted
> > (Surveyor said it had leached or something). I let the yard I bought the
> > boat from do it. Didn't know enough about anything at the time. (still
> > don't!)
> >
> > I have never had good performance from the engine. Despite a complete
> > strip down and re-build with new bearings seals etc. etc.and spot on
> > timing under load - set by timong gun. I make max 2 to 3 Knots and it
> > always sounds quite laboured and flat when under load, although it is
> > perky and responsive out of gear.
> >
> > I was reading the engine spec the other day. It rates the engine as 10hp
> > at 1650 rpm. I put a timing gun on it the other day. At full throttle
> > under load I never get above 800 rpm.
> >
> > So is it possible that the yard put the wrong size prop on? How do I
find
> > out what size prop I have at the moment. I have a bit of software to
> > recomend the correct size.
> >
> > comments and speculation most welcome
> >
> > Simon
>
> Take a look at http://www.piranha.com/. There is a few pages that provide
a
> sort of tutorial to help you discover the right size of propellor for your
> application.
>
> --
> ********************************************************************
> Paul E. Bennett ....................
> Forth based HIDECS Consultancy .....
> Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
> Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
> Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
> ********************************************************************

Cant be terribly hard.... mark shaft coupling..... turn engine 1rev.( in
forward gear).. how far did prop turn?

Then phone lancing marine.. tell him boat, engine and ratio ...he will tell
you prop required.

I have only a week ago, researched prop prices... and bought my pair from
him as he was 20% cheaper than any other quotes i found.

M O F W I W

Ian Sandell · Joined: 17 Aug 2007 Posts: 14

On Mon, 13 Sep 2004 20:43:29 +0100, Guy Fawkes wrote:

>Simon Neal wrote:
>
>> Hi
>>
>> I have a 25ft fin keel Marcon Tomahawk. I have a Stuart turner 10hp two
>> stroke engine. When I first bought the boat I had a new prop fitted
>> (Surveyor said it had leached or something). I let the yard I bought the
>> boat from do it. Didn't know enough about anything at the time. (still
>> don't!)
>>
>> I have never had good performance from the engine. Despite a complete
>> strip down and re-build with new bearings seals etc. etc.and spot on
>> timing under load - set by timong gun. I make max 2 to 3 Knots and it
>> always sounds quite laboured and flat when under load, although it is
>> perky and responsive out of gear.
>>
>> I was reading the engine spec the other day. It rates the engine as 10hp
>> at 1650 rpm. I put a timing gun on it the other day. At full throttle
>> under load I never get above 800 rpm.
>>
>> So is it possible that the yard put the wrong size prop on? How do I find
>> out what size prop I have at the moment. I have a bit of software to
>> recomend the correct size.
>>
>> comments and speculation most welcome
>>
>> Simon
>
>
>http://www.surfbaud.co.uk/download.php?view.5
>
>it will answer all your questions.

Not quite. As Alec said, you must know gearbox ratio.

Ian

Guy Fawkes · Joined: 17 Aug 2007 Posts: 6

Ian Sandell wrote:

>>
>>http://www.surfbaud.co.uk/download.php?view.5
>>
>>it will answer all your questions.
>
> Not quite. As Alec said, you must know gearbox ratio.
>
> Ian

yes quite, because it also tells you how to measure an unknown gearbox
ratio.

Ian Sandell · Joined: 17 Aug 2007 Posts: 14

On Tue, 14 Sep 2004 22:57:19 +0100, Guy Fawkes wrote:

>Ian Sandell wrote:
>
>
>>>
>>>http://www.surfbaud.co.uk/download.php?view.5
>>>
>>>it will answer all your questions.
>>
>> Not quite. As Alec said, you must know gearbox ratio.
>>
>> Ian
>
>
>yes quite, because it also tells you how to measure an unknown gearbox
>ratio.

Apologies then, but I didn't see it in earlier version and a quick
look at this version I cant see it. I suppose it's there somewhere.

Ian

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