Outboard confusion

[winsbury]

We currently have a bulletproof and reliable but old 8hp Mariner Sailmate 2 stroke in well as our main engine (approx 2 ton bilge keel 23ft loa sailboat .) Problem is that its noisy and smelly and almost always sets the fire alarm off and makes me feel a bit sick after a while so is far from ideal for a long run but it drives the boat well even against the strong currents around Langstone at 5.5 - 6 knts at full throttle.

I'm therefore thinking of changing to something cleaner and quieter but dont want anything overly heavy that will affect boats balance ( 6 - 8 hp I believe is the designers recommended size for our boat.) I'm thinking a 8 or 9.9 hp four stroke Mercury / Mariner but have some questions for the more experienced and less sales commission motivated panel before parting with around two grand:

1. What is the difference between Sailmate / high thrust and the standard engines/props .
2. what on earth is the difference between the 8 and 9.9hp engines - on paper they are the exact same spec and weight except for power rating... do the 9.9s have a larger prop so would rev lower for the same thrust as a 8hp ?
3. will a 4 stroke be 'much' quieter than the 2 stroke
4. will the fumes be any less potent
5. The existing 8hp engine rating is presumably in old money ( power at prop versus crank or something like that ) so how does that compare with power ratings on new engines.
6. How does one select the correct HP for any given boat - is there a formula ?

Any or all queries answered would be much appreciated.

 

[VicS]

1. Id expect the Sailmate prop to be a smaller pitch and probably a lager diameter and/or larger blade area...

2. There could be many differences from a simple throttle limiter on the 8 to different carb jets, different carb entirely, different manifold and porting.
( My 6 hp Evinrude at first glance is the same as its 8hp cousin but it is not even a viable proposition to uprate it when you get down to the details).
You may well find that the 9.9 is rated at higher revs than the 8 hp.

3 often they are quieter

4 The fumes will not be oily but if you don't vent the relief port over board then you may well have a similar problem. Fumes and noise are downsides of outboards in wells

5. The power ratings were changed with the introduction of ICOMIA 28/83 from being quoted at the crankshaft to being quoted at the prop shaft. Some manufactures may have quoted propshaft figures before 1983 though. (I'd guess about 2 hp difference at the power ratings you are talking about)

6. No formula that I am aware of. Manufacturers advice and asking on a good internet forum.

If you are happy with 8hp there is no reason to increase it esp considering that the fourstroke will most likely be heavier .. perhaps significantly heavier.

Lower fuel consumption is a good reason to choose a 4 stroke.

 

[Lakesailor]

4 The fumes will not be oily but if you don't vent the relief port over board then you may well have a similar problem. Fumes and noise are downsides of outboards in wells

That is probably the major problem. You are much closer to the motor than if it's hung on the stern so it's noisier and the fumes are more likely to be sucked back into the cockpit.

The only boat with an engine in a well that doesn't seem to suffer these problems is the admirable Anderson 22.

 

[alahol2]

If you are likely to go up to 9.9HP then you really should be looking at the Yamaha 9.9 High Thrust outboard. We had one on a 32ft catamaran and it was superb. It has a larger prop diameter, larger prop area and lower pitch, all designed to push heavy displacement boats. To be honest it would be overkill on a 23ft boat but I don't know if there is a smaller equivalent from any other maker. And yes, a 4 stroke should be much quieter and less smoky than a 2 stroke.

 

[onesea]

If you are likely to go up to 9.9HP then you really should be looking at the Yamaha 9.9 High Thrust outboard. We had one on a 32ft catamaran and it was superb. It has a larger prop diameter, larger prop area and lower pitch, all designed to push heavy displacement boats. To be honest it would be overkill on a 23ft boat but I don't know if there is a smaller equivalent from any other maker. And yes, a 4 stroke should be much quieter and less smoky than a 2 stroke.

Over kill with 4 strokes might be a good thing, they do not like hard work at 100% I found. Certainly the last 20% on my last boat made the volume double, plus when you want that extra punch its there...

 

[Rigger Mortice]

We currently have a bulletproof and reliable but old 8hp Mariner Sailmate 2 stroke in well as our main engine (approx 2 ton bilge keel 23ft loa sailboat .) Problem is that its noisy and smelly and almost always sets the fire alarm off and makes me feel a bit sick after a while so is far from ideal for a long run but it drives the boat well even against the strong currents around Langstone at 5.5 - 6 knts at full throttle.

I'm therefore thinking of changing to something cleaner and quieter but dont want anything overly heavy that will affect boats balance ( 6 - 8 hp I believe is the designers recommended size for our boat.) I'm thinking a 8 or 9.9 hp four stroke Mercury / Mariner but have some questions for the more experienced and less sales commission motivated panel before parting with around two grand:

1. What is the difference between Sailmate / high thrust and the standard engines/props .
2. what on earth is the difference between the 8 and 9.9hp engines - on paper they are the exact same spec and weight except for power rating... do the 9.9s have a larger prop so would rev lower for the same thrust as a 8hp ?
3. will a 4 stroke be 'much' quieter than the 2 stroke
4. will the fumes be any less potent
5. The existing 8hp engine rating is presumably in old money ( power at prop versus crank or something like that ) so how does that compare with power ratings on new engines.
6. How does one select the correct HP for any given boat - is there a formula ?

Any or all queries answered would be much appreciated.

I've got the service manual in front of me and, as usual the answer to some of your question are a bit complex!

1. The Sailmate prop is a high reverse thrust prop 9.75" dia 6.5" pitch. They list 5 props, identical ones across the range from 6hp up to 9.9/10hp. At one end of the range is a 9" x 9" prop at the other end is a 9.75" x 5.5" but only one of them is described as a high reverse thrust. It's difficult to say which of the others would be described as the "standard" prop; it may vary from market to market

2. The main differences are the jets in the carbs except for post 1995 engines when the capacity of the 9.9 increased from 209cc to 262cc. There are other small differences but little of substance. The prop for the 9.9 would be the same, but the engine revs are higher. 4500-5500 for the 8hp. 5000-5500 for the 9.9hp

3. In my experience a four stroke is a lot quieter.

4. In my experience the fumes from a four stroke are a lot lower. AFAIK not only are you burning less oil but the engines are also more efficient so the exhaust is cleaner irrespective of the oil. But, regardless of the reasons, there is a noticeable difference

5. The manual quotes the 8hp Sailmate power as "8(5.9)" . The bracketed figure is KW; I assume that the way it is measured hasn't changed over the last few years, but I don't know.

6. Thousands have asked that question. Nobody has come up with a universally accepted answer!

 

[TSB240]

If you are considering changing from 2 stroke to 4 stroke be very careful as In my experience the size of the new 4 stroke designs will not fit the wells that were typically designed for the leg and prop of a 2 stroke.

The largest 2 stroke that will fit the well of our TS is 6hp. There is no twin cylinder 4 stroke similar to the tohatsu 9.8 2 stroke that will fit.

Reference the smoke in the cockpit the tohatsu 2t and its family derivatives have the option of an add on exhaust relief from the top of the leg that ducts some of the exhaust through a small pipe in the transom. This in my experience makes a well mounted 2t much more acceptable.

Be warned the noise of an overworked single cylinder 4 stroke is far worse than a silky smooth twin working at lower revs.

 

[BruceDanforth]

Is that really a problem with a modern engine?

The engines have to meet ultra low emissions standards (EPA / CARB). I'm never really aware of fumes getting sucked into the cockpit. I think it would be more of a problem for older engines.

That is probably the major problem. You are much closer to the motor than if it's hung on the stern so it's noisier and the fumes are more likely to be sucked back into the cockpit.

The only boat with an engine in a well that doesn't seem to suffer these problems is the admirable Anderson 22.

 

[winsbury]

Thanks people, certainly a couple of very pertinent points raised : the size of the well for example could be an issue as even the existing engine is tight fit. As to the relief port I didnt know about that at all but I imagine thats why theres quite a lot of exhaust above the waterline when it first starts which goes away when up to revs and the exhaust is then venting efficiently via the prop...possible redirecting this would indeed solve or reduce the fumes issue, Ill take a closer look to see if this could be vented overboard somehow, at low revs it sometimes chokes itself on the fumes so there would be a second reason to do this.

The engines I cited are a few kilos heavier than the existing engine but nothing like as heavy as other brands, most notably the hondas seem to weigh in very heavy. The 9.9 weighs the same as the 8 so given the it would not need to be driven at full revs and the extra power would negate any loss in performance due to the power measurement method that sounds like the way to go to me.

Prop selection seems to be a minefield and very complex, is it normal to have to buy a different prop once the engine has been mounted and performance with the standard prop has been checked or will the dealer put an appropriate prop on at point of sale ?

Better armed now for a conversation with the sales guy so will hopefully get this right.

 

[ninky]

I'd advise talking to a couple of outboard dealers - okay so they have some sort of vested interest but if you talk to more than one then you get a different point of view. They have better advice as they are dealing with the engines all the time and know which models develop problems etc. I ended up with an engine that wasn't ideal after taking advice from this forum - not blaming those who gave advice in good faith, but you don't really know what qualifications people have, or experience on here - and buying a new engine is costly. I should have done my research with some outboard dealerships and service centres. One thing I found out is that some of the lower HP models are basically the same as the higher ones, but de-powered. So you may as well get the higher one when this is the case. Saildrive seems to be the way to go. I'd say tohatsu saildrive 6hp, poss with separate tank, is a good option for you - but, like I say, don't just take the word of anyone on here.

Nicola

 

[TSB240]

Prop selection seems to be a minefield and very complex, is it normal to have to buy a different prop once the engine has been mounted and performance with the standard prop has been checked or will the dealer put an appropriate prop on at point of sale ?

Better armed now for a conversation with the sales guy so will hopefully get this right.

Dealer will normally specify the correct prop. I am sure in your case that he will recommend the appropriate saildrive prop given the size and weight of your boat. I have fitted a 4 blade Solas aftermarket prop to ours and it has transformed the performance. It has massive grip on the water and means that you dont get any egg whisk effect that you might with a standard prop. It also provides more punch into short steep wind against tide chop.

 

[VicS]

Thanks people, ............................................... will hopefully get this right.

Re fumes in a well

All the while the engine is running it will be pushing out some exhaust gas via the back pressure relief port, a little water usually also. TSB240 tells us that Tohatsu engines can be fitted with an accessory to duct these fumes away.

When you first start, when the engine is idling, maybe also when moving slowly too, exhaust gas rises to the water surface in the well. . With a decent bit of boat
speed of course the gases don 't surface until some distance behind the boat.


In extreme cases engines can "inhale" and choke on their own exhaust gas if it is trapped in the well by a cover etc.


Oh another point to keep in mind is that "sail" versions of outboards usually/ sometime/may only be supplied as long shaft engines. If you only want a standard shaft for your well you may have to buy the high thrust sail prop specially as an alternative to the standard prop.

 

[davidpbo]

O.P. I was asking similar of a salesman recently.

We have an 8HP Mercury in a well with a relief pipe through the transom. My signature was written last week, we have been having some problems with but hopefully it is fixed now after a sojourn with mender.

Generally speaking fumes were only a problem if stationary. It is a noisy 2 stroke though.

The relief pipe I have is an 8mm copper pipe.

 

[C08]

I replaced a 30HP 2 stroke Tohatsu engine for a 20Hp 4 stroke Tohatsu on the basis of reduced noise levels and this has been a total success. The engine is so quite that at low revs I have to look at the rev counter to check it is going! You have lots of (mostly) good advice and the points about the bigger size and weight are well made. My 20HP 4 stroke is a little bigger and a lot heavier than the 30HP 2 stroke it replaced. There is one thing not mentioned and that is that different manufacturers use different gear ratios. Best of all are the saildrive engines which are really higher geared and swing a bigger prop but there are differences in the long shaft gearing between different makers. I ended up using a non-saildrive engine but with an extra long shaft (no saildrive are made in 20HP size) and the engine has performed perfectly for us on a 3ton cat. I think the Tohatsu has a higher gearing than some other makers anyway.

 

[VicS]

I replaced a 30HP 2 stroke Tohatsu engine for a 20Hp 4 stroke Tohatsu on the basis of reduced noise levels and this has been a total success. The engine is so quite that at low revs I have to look at the rev counter to check it is going! You have lots of (mostly) good advice and the points about the bigger size and weight are well made. My 20HP 4 stroke is a little bigger and a lot heavier than the 30HP 2 stroke it replaced. There is one thing not mentioned and that is that different manufacturers use different gear ratios. Best of all are the saildrive engines which are really higher geared and swing a bigger prop but there are differences in the long shaft gearing between different makers. I ended up using a non-saildrive engine but with an extra long shaft (no saildrive are made in 20HP size) and the engine has performed perfectly for us on a 3ton cat. I think the Tohatsu has a higher gearing than some other makers anyway.

I have not come across any variation in gear ratios between standard and "sail" versions of the same engine ( although that does not mean there is none ) the overall gearing ratio change is done by using props of different pitch. The smaller pitch of the "sail" props actually producing a lower, not higher, overall ratio. This results in the engine running at higher revs and consequently producing more power at the same boat speed with the "sail" prop The downside is of course it makes it noisier and probably a little more thirsty

 

[alahol2]

I have not come across any variation in gear ratios between standard and "sail" versions of the same engine ( although that does not mean there is none ) the overall gearing ratio change is done by using props of different pitch.

The only one I know that uses different gear ratios is the Yamaha High Thrust 9.9 at nearly 3:1 compared to the nearly 2:1 of the 'standard' 9.9.

 

[Rigger Mortice]

The Mariner 2 strokes appear to have the same gearbox ratio throughout the 6-15 hp range.

 

[winsbury]

Just thought I'd add an update as I think I saved myself a couple of grand for the price of a few feet of gas tubing....replacing the anode I noticed a small hole with sooty residue under the crankcase. Blowing into it with a bit of 8mm gas pipe confirmed it was linked to the exhaust as air came out of the prop hub. Hooking the same bit of copper pipe to some out of date flexible gas pipe and dangling it over the side before starting the engine gave the most agreeable result....all the exhaust fumes vented successfully outside the cockpit, no fire alarm any more, and the engine ran sweet as a nut developing more power than previously.

Thanks to davidpbo for the tip.

 

[langstonelayabout]

We currently have a bulletproof and reliable but old 8hp Mariner Sailmate 2 stroke in well as our main engine (approx 2 ton bilge keel 23ft loa sailboat .) Problem is that its noisy and smelly and almost always sets the fire alarm off and makes me feel a bit sick after a while so is far from ideal for a long run but it drives the boat well even against the strong currents around Langstone at 5.5 - 6 knts at full throttle.

I'm therefore thinking of changing to something cleaner and quieter but dont want anything overly heavy that will affect boats balance ( 6 - 8 hp I believe is the designers recommended size for our boat.) I'm thinking a 8 or 9.9 hp four stroke Mercury / Mariner but have some questions for the more experienced and less sales commission motivated panel before parting with around two grand:

1. What is the difference between Sailmate / high thrust and the standard engines/props .
2. what on earth is the difference between the 8 and 9.9hp engines - on paper they are the exact same spec and weight except for power rating... do the 9.9s have a larger prop so would rev lower for the same thrust as a 8hp ?
3. will a 4 stroke be 'much' quieter than the 2 stroke
4. will the fumes be any less potent
5. The existing 8hp engine rating is presumably in old money ( power at prop versus crank or something like that ) so how does that compare with power ratings on new engines.
6. How does one select the correct HP for any given boat - is there a formula ?

Any or all queries answered would be much appreciated.

1 - The difference between the sail power/mate engines and standard ones is that they have a far larger, finer pitched prop. They usually have a charging set for your boat's battery too...
2 - The 2 engines have a different carb jet and parameters within the electronics modules.
3 - The 4 stroke will be noticeably quieter than the 2 stroke, with only a puff of blue smoke at startup. Otherwise it'll be far cleaner.
4 - Much, much less potent. (But remember that it'll be a tad heavier at the rear of your cockpit too...)
5 - Which sort of horsepower? http://en.wikipedia.org/wiki/Horsepower
6 - I believe the suck it and see approach works. For my bilge keeled Pegasus 700 a good Mercury sail power 4 2-stroke (lighter weight, big prop) was bought to get rid of the Mercury 9.9. The 9.9 was about 70kg in the wrong place and not missed. The 4 is fine and easily enough for the boat.

Oh, and I found that I had to remove the lower 'leg' of the outboard to get it through the Pegasus 700's stern outboard well. Do this ashore and without the pressure of a rising tide to worry about...

 

[winsbury]

1 - The difference between the sail power/mate engines and standard ones is that they have a far larger, finer pitched prop. They usually have a charging set for your boat's battery too...
2 - The 2 engines have a different carb jet and parameters within the electronics modules.
3 - The 4 stroke will be noticeably quieter than the 2 stroke, with only a puff of blue smoke at startup. Otherwise it'll be far cleaner.
4 - Much, much less potent. (But remember that it'll be a tad heavier at the rear of your cockpit too...)
5 - Which sort of horsepower? http://en.wikipedia.org/wiki/Horsepower
6 - I believe the suck it and see approach works. For my bilge keeled Pegasus 700 a good Mercury sail power 4 2-stroke (lighter weight, big prop) was bought to get rid of the Mercury 9.9. The 9.9 was about 70kg in the wrong place and not missed. The 4 is fine and easily enough for the boat.

Oh, and I found that I had to remove the lower 'leg' of the outboard to get it through the Pegasus 700's stern outboard well. Do this ashore and without the pressure of a rising tide to worry about...

we should probably put the Pegasus specific stuff on the Owners Group website but fwiw, the anti-cavitation plate on the 8hp had previously been reduced in size a little to allow fitting/removal from on deck but it is still a tight squeeze and takes some wiggling to get it through - that said I prefer that to faffing about removing the leg to do it. Thankfully in my attempts to solve the problems all of which are now good thanks to the pipe detailed in previous post I have :

1) Acquired a fairly new 6hp 4-stroke Mariner, albeit without the sailmate prop ( but does have an alternator ) , so will have an experiment with that at some point as its about 15kg lighter than the 8hp 2-stroke so should offer better fuel economy, boat balance and should be quieter

and

2) found all the 9.9's on the market have the problem you describe with the anticavitation plate being far too large to fit through the well opening without serious modification or taking the leg off, neither of which would preserve the warranty on a new engine.

Nevertheless, great to hear a 4hp works for you, sounds like the 6hp will be okay if I can find a suitable prop for it.