Yamaha 5HP converting for sailing dayboat use!

Zagato

Zagato

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Firstly I have already had a Tohatsu and Marina Sailmate (same engine/ carb made in China apparently ) and had long term problems with both (not gummed up fuel etc, well aware for years on all that, I use Aspen fuel also now, carbs are now routinely changed under warranty bla bla) ...

OK now that is out of the way. I know Yamaha build quality from owning their bikes... they still make their outboard engines in Japan so I would like to buy a Yamaha this time BUT it will be for a little 400KG, 19' long sail boat. Would changing the prop pitch be a sound option as they don,t sell a 'sailmate' option. I understand I may get higher revs which and I am not bothered about and the exhaust fumes when reversing possibly causing cavitation, I can row for close manoeuvres.

I am selling a brilliant Honda 8HP, so reliable and smooth BUT sadly it is too heavy for my boat let alone the extra power which is ineffective on the hull!
 
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Zagato said:
Firstly I have already had a Tohatsu and Marina Sailmate (same engine/ carb made in China apparently ) and had long term problems with both (not gummed up fuel etc, well aware for years on all that, I use Aspen fuel also now, carbs are now routinely changed under warranty bla bla) ...

OK now that is out of the way. I know Yamaha build quality from owning their bikes... they still make their outboard engines in Japan so I would like to buy a Yamaha this time BUT it will be for a little 400KG, 19' long sail boat. Would changing the prop pitch be a sound option as they don,t sell a 'sailmate' option. I understand I may get higher revs which and I am not bothered about and the exhaust fumes when reversing possibly causing cavitation, I can row for close manoeuvres.

I am selling a brilliant Honda 8HP, so reliable and smooth BUT sadly it is too heavy for my boat let alone the extra power which is ineffective on the hull!
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Basic prop will be fine, I changed mine on a 3.5hp from plastic to a metal one, ( I have an 18ft and 3.5hp is plenty, obviously sans reverse) but on the bigger engines they are all metal, sail drive prop is a much finer pitch, but when I had a drascombe it had a Yamaha with stock propeller.
 
Std prop is fine ..... yes it revs a bit higher ... but that's not a problem

I had a bog standard Yamaha 5 (the air cooled version) on my Snapdragon 23 years ago .... then stupidly sold it .... replaced it with a Mercury 7.5 Saildrive. Fantastic motor - but so heavy with that reduction gearbox etc.

I have a Johnson 4.5 twin on my 5.5m weekender sailboat .... excellent ....
 
Yes i agree with you VicS. If you put a sailmate prop on the Yamaha it revs higher apparently. The gearbox ratio on the Marina Sailmate is different!

I am wondering wether to stick to the ordinary prop on the Yamaha. The Drascombe Lugger is not exactly a displacement hull in the yacht sense. It's only 330KG, 19' with a 9" draft, centre plate up! It would avoid the higher revs also...
 
I use the standard aluminium prop that came with the 2.5 HP 4-stroke Yamaha on my 16-foot Wayfarer and have no problems at all. It pushes our heavily-loaded cruising dinghy along at 4 knots at half revs. with two people aboard plus camping/cruising gear.
 
northwind said:
Basic prop will be fine, I changed mine on a 3.5hp from plastic to a metal one, ( I have an 18ft and 3.5hp is plenty, obviously sans reverse) but on the bigger engines they are all metal, sail drive prop is a much finer pitch, but when I had a drascombe it had a Yamaha with stock propeller.
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Probably this.

I spent £120 on a high thrust prop for my 5hp Mariner 2T and I'm not convinced it was worth it over a £35 standard prop. Whatever the OP does he should try a standard prop first for a season.

Having said that I wouldn't be a avoiding a high thrust prop either if it's free with the engine.

I'll lend my voice to the 'high thrust prop' = lower gear - turns faster for more power at lower speeds.
 
Refueler said:
You could be right actually ... bit of brain fade there ...

The saildrive prop should be slightly less pitch to give greater thrust and less emphasis on speed
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My Evinrude Yachtwin has a 23.5 x 16.5 cm prop compared with 21.6 x 22.9 cm for the standard prop so little larger in diameter but quite a bit less in pitch. It also has big "Mickey Mouse ear" blades.
The standard model is a long shaft , if you see what I mean.
It also has a modified exhaust which prevents exhaust gases being drawn into the prop when going astern. Therefore has good thrust astern
 
Interesting thanks all. I think my emphasis would be less about slow speed manouvering thrust but more on efficiency fighting tidal currents in Poole, Chichester etc and cruising under power around the Solent. I would think the hull is more akin to a speed boat than sailboat so would I be right in saying the standard prop would be more efficient at speed and more efficient with less resistance with smaller blades and lower revs.
 
Zagato said:
Interesting thanks all. I think my emphasis would be less about slow speed manouvering thrust but more on efficiency fighting tidal currents in Poole, Chichester etc and cruising under power around the Solent. I would think the hull is more akin to a speed boat than sailboat so would I be right in saying the standard prop would be more efficient at speed and more efficient with less resistance with smaller blades and lower revs.
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Yes, the standard prop will be optimized for higher speeds. The high thrust prop will be optimized towards pushing a sluggish bilge keeler at 4kts.
 
Zagato said:
Interesting thanks all. I think my emphasis would be less about slow speed manouvering thrust but more on efficiency fighting tidal currents in Poole, Chichester etc and cruising under power around the Solent. I would think the hull is more akin to a speed boat than sailboat so would I be right in saying the standard prop would be more efficient at speed and more efficient with less resistance with smaller blades and lower revs.
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What boat is it?
 
Zagato said:
Interesting thanks all. I think my emphasis would be less about slow speed manouvering thrust but more on efficiency fighting tidal currents in Poole, Chichester etc and cruising under power around the Solent. I would think the hull is more akin to a speed boat than sailboat so would I be right in saying the standard prop would be more efficient at speed and more efficient with less resistance with smaller blades and lower revs.
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My Yamaha was pushing Snapdragon 23 in / out of Langstone Harbour ..... and round Solent ..... when tide was running full bore at Langstone then staying close to beachline was needed to avoid its full force. But that applies to most small boats.
 
northwind said:
What boat is it?
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Drascombe Lugger, as previously mentioned, 8" draft min, flatish bottom, more speed boat than displacement sailing boat I should think. Max hull speed is about 5knots I believe. The nose just dives apparently if you over power it. I think the conclusion we are saying is the standard prop for the strong Solent currents...
 
Zagato said:
Drascombe Lugger, as previously mentioned, 8" draft min, flatish bottom, more speed boat than displacement sailing boat I should think. Max hull speed is about 5knots I believe. The nose just dives apparently if you over power it. I think the conclusion we are saying is the standard prop for the strong Solent currents...
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Lugger is not what I would term a motorboat hull ... its basically an overgrown dinghy.

Standard prop for Solent currents ? Not what we are saying. What we are saying is the difference of props is not something to overly concern about.

Lets illustrate SPEED vs THRUST.

High pitch prop will have high max speed but often acceleration can be slower on a displacement hull due to prop cavitating. Eventually it will reach drag vs speed balance.
Low pitch prop will have low max speed but better acceleration.

Good examples are Tugs vs high powered offshore boats ...

The Tug can be stationary and exerting TONS of thrust against a ships side. Once free to move - its top speed is maybe 10kts if lucky.
Same HP but high pitch props on power boat ... 70 ... 80 kts or more but useless for pushing that ship.

So lets take a harbour entrance .... say a 5kt tide race running.

If your boat has a standard prop and capable of 6kts in still water .. you'd expect to have net 1kt speed over ground. But in fact you will have less than 1kt due to prop higher pitch for speed rather than thrust.
If your boat has a saildrive prop capable of 5.5kts in still water - you probably will find same speed over ground due to its better thrust profile.

But at end of day ... a bog standard Yamaha 5 on back of your Lugger will be fine.
 
I havent much experience with saildrive outboards compared to conventional. What I do have lots of experience of is repairing outboards that have been run on Aspen.
Irrespective of what manufacturers say it is no goid to use regularly on modern 4 strokes
 
Steve65 said:
I havent much experience with saildrive outboards compared to conventional. What I do have lots of experience of is repairing outboards that have been run on Aspen.
Irrespective of what manufacturers say it is no goid to use regularly on modern 4 strokes
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On the subject of which it's worth a reminder that Esso's Synergy Supreme 99 is (typically) zero Ethanol.

Fuels Frequently Asked Questions | Esso
 
Steve65 said:
I havent much experience with saildrive outboards compared to conventional. What I do have lots of experience of is repairing outboards that have been run on Aspen.
Irrespective of what manufacturers say it is no goid to use regularly on modern 4 strokes
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What problems does it cause? Very interested to hear... thanks. What do you recommend fuel wise and maybe an additive?
 
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