Tohatsu 6 long shaft

[mikehoyt]

I have 27 foot sailboat, 8.5 foot beam, 3800 lbs displacement. Is a racing boat. Currently powered by 1982 Johnson Seahorse 4.5 long shaft approx 55 lbs

Am considering upgrading to more power but weight is a critical consideration. Cannot exceed 60 lbs.

Would the Tohatsu 6HP be a good choice for this situation? Will there be a significant increase in power to push the boat against wind, waves or current?

Thanks

Mike

 

[TOHATSU GURU]

Re: Tohatsu 6 long shaft

Both engines are too small for the load, however, the Tohatsu will push it with the 5.9999 pitch pig propeller. Going from a 2-stroke to a 4-stroke will be a big disapointment for you though. Other than noise level and fuel economy the 2-strokes are far superior.

 

[pvanv]

Re: Tohatsu 6 long shaft

Gotta agree with Elvin in that your boat deserves an 8 or 9.8. I hang 9.8's on Catalina 25's all the time. But at the hefty 82 pounds for that 2-cylinder 9.8, your second-best rig would be the 1-cylinder 6 hp sail pro, which has UL (25") shaft, alternator setup, and elephant-ear (EE) high-thrust prop. If you are sure that you prefer 20" shaft, your dealer can configure a Long to be the same, but 5" shorter.

The 4-strokes have a significantly different torque and power curve from the 2-strokes of the pre-EPA-mandate days. So, as Elvin mentioned you may not be too impressed with the 6 hp vs your old 4.5 hp, until you get into the upper RPM area. Depending on the year of your old OMC, you may have 4.5 hp at the crank. All modern OB's are rated at the prop, so the old 4.5 may have been delivering less than 4 hp to the water. Then again no matter what, it will use less fuel, and will be a lot quieter at speed.

 

[mikehoyt]

Re: Tohatsu 6 long shaft

I guess that not everybody is super familiar with sailboats. Our boat is a very light race boat. It is a J/27 which is 3800 lbs. It is a race boat and not a cruiser like a Catalina 25 and is significantly lighter than a Catalina 25. The J/27 has a very low freeboard and is very slippery thru the water. Consequently it can use a 15" short shaft motor but a 20 inch long shaft is plenty deep to avoid any cavitation.

Weight on the ends of these boats is a no no. One day I did try a 2004 Johnson 2 stroke 9.9 short shaft as my engine was in the shop. Is far too heavy for the boat and when opened up only dug the stern in. Very unsuitable engine.

With the J/27 the major class consideration is minimum size not maximum size. Am not allowed to use anything under 4 hp. The boat initially came with a short shaft 1988 Johnson Seahorse 4hp. The 4.5 was stumbled on by accident in its long shaft configuration and had far fewer hours than the original engine - so I simply traded them.

The heaviest I am willing to go is 60 lbs. Even that is pushing it. A 25 inch shaft is out of the question as it sticks out way too far when out of the water and has too much weight too far aft. With the low freeboard of this boat the 20" is perfect. I know there is a new 6hp Tohatsu coming for 2011 with alternator and internal tank with external tank connector that comes in 15, 20 and 25 inch shafts. The 20 inch version would be the one I would want.

A second option if that new configuration is not available is a 2010 4hp Tohatsu 20 inch reconfigured with high thrust prop, alternator etc... which I have been told will basically be same power as the 6hp.

So again the question - since the older engine had hp rated at bottom of power head and the new ones at prop and since the old engine did not have a high thrust prop and since all engines on my boat are typically run wide open against a wind will the 6 hp offer a significant difference to the 1982 4.5?

Note that unless there is an ultralight 8 or 9.9 that is under 60 lbs these are not even remotely considered as this is for a racing sailboat.

Thanks again

Mike

 

[TOHATSU GURU]

Re: Tohatsu 6 long shaft

I guess that not everybody is super familiar with sailboats. Our boat is a very light race boat. It is a J/27 which is 3800 lbs. It is a race boat and not a cruiser like a Catalina 25 and is significantly lighter than a Catalina 25. The J/27 has a very low freeboard and is very slippery thru the water. Consequently it can use a 15" short shaft motor but a 20 inch long shaft is plenty deep to avoid any cavitation.

Weight on the ends of these boats is a no no. One day I did try a 2004 Johnson 2 stroke 9.9 short shaft as my engine was in the shop. Is far too heavy for the boat and when opened up only dug the stern in. Very unsuitable engine.

With the J/27 the major class consideration is minimum size not maximum size. Am not allowed to use anything under 4 hp. The boat initially came with a short shaft 1988 Johnson Seahorse 4hp. The 4.5 was stumbled on by accident in its long shaft configuration and had far fewer hours than the original engine - so I simply traded them.

The heaviest I am willing to go is 60 lbs. Even that is pushing it. A 25 inch shaft is out of the question as it sticks out way too far when out of the water and has too much weight too far aft. With the low freeboard of this boat the 20" is perfect. I know there is a new 6hp Tohatsu coming for 2011 with alternator and internal tank with external tank connector that comes in 15, 20 and 25 inch shafts. The 20 inch version would be the one I would want.

A second option if that new configuration is not available is a 2010 4hp Tohatsu 20 inch reconfigured with high thrust prop, alternator etc... which I have been told will basically be same power as the 6hp.

So again the question - since the older engine had hp rated at bottom of power head and the new ones at prop and since the old engine did not have a high thrust prop and since all engines on my boat are typically run wide open against a wind will the 6 hp offer a significant difference to the 1982 4.5?

Note that unless there is an ultralight 8 or 9.9 that is under 60 lbs these are not even remotely considered as this is for a racing sailboat.

Thanks again

Mike

The one engine you do not want is the 2011 model. That one will be two lbs heavier than the 2010. The 4 hp is the same story...It's two lbs heavier than the standard 5 or 6 due to the integral tank...And that does not include the fuel that would be hanging off the stern in an integral model. The problem with ANY four-stroke, one cylinder engine, is that has a hard time developing RPM when pushing a load. Planning hull, displacement hull, no difference. So, you will have marginal performance compared to an older 2-stroke design as they develop power easier along their curve. IE If a 4-stroke CAN develop its rated RPM with a low pitched prop it's fine. However, with anything approaching 3000 lbs, current and windage....You will probably never see the rated hp. So, people who know about this stuff will suggest that you to go to a 2 cylinder, 4-stroke to avoid the one cylinder issue or get the most hp you can for the weight (the 6 Tohatsu) and live with performance about equal to what you have now. Depending on all the variables there could be a half knot variance either way between the two engines.

 

[pvanv]

Re: Tohatsu 6 long shaft

Yep, Elvin is right. The integral tank will add a couple of pounds aft of the transom, where you don't want it. On race-only J27's for Lake Erie, we rig the 4/5/6 in 15" configuration, but on Lake Ontario, with the longer swells, we spec the 20" shaft due to porpoising. My neighbor's J27 (in Wilson, NY) is equipped with a 6 hp long, and it works pretty well.

Regardless, you will need to develop max RPM in order to see the top HP, so you will definitely want the EE prop. The last 2 hp is developed in the last 1-2,000 RPM of the power curve, so low pitch is a must.

If I were rigging your boat, I would use the MFS6B in 20", external tank (that you can toss below when racing), with EE prop, and consider the alternator optional, as you will only need it to offset any running-light draw for night returns to the dock or mooring.

 

[mikehoyt]

Re: Tohatsu 6 long shaft

Thank you both.

What is the EE prop? I have spoken with someone here who had stated the 4 could be configured by adding the following to be same power as the 6 ... Is that the EE prop he suggested?

MFS4BL
Alt. kit
Rectifier kit
Carb
Prop (high thrust)

Integral fuel tank nice but not amust. For quick trips saves dragging external tank around.

Previous boat had a Honda BF75 from 1979. Essentially similar to 9.9 of the era. Was a 4000 lb boat but much more drag thru the water, more freeboard and more windage. That engine had much more power - is it similar in being 4 stroke to the comments above re getting up to high RPMs?

Is there another engine on the market that is 2 stroke and light in the under 60 lb market? I have not found any and Honda 5hp is only model light enough and Yamaha also heavier. Am I missing any?

Had a Johnson Seahorse 4hp short shaft (1988) when I got teh boat and it was far less suitable than the 4.5 long shaft I now have.

We sail in the Northumberland Strait between Nova Scotia, Prince Edward Island and New Brunswick. Usually 1 - 2 knots tidal current and when windy close choppy waves.

Mike

 

[TOHATSU GURU]

Re: Tohatsu 6 long shaft

Canada still may have some two-strokes running around that you can pick up, but none in the U.S. To turn a 4 into the 6 just requires a new 6 hp carb. To make a 4 into a Sail 6 you would need the other stuff you listed. The part number for the 5.9999 pitch prop( Paul calls it an elephant ear, I call it a pig prop) is 399B645121M. It will also cost you a lot more to convert the 4 than buying the Sail 6. The reason I stressed the integral tank weight gain is that the Sail 6 in the 25" weighs less than the two pounds of the integral tank...

 

[mikehoyt]

Re: Tohatsu 6 long shaft

Thanks

You guys are a wealth of knowledge.

Note that the current Johnson is Seahorse model J5RHLCNR 4.5hp 20 inch shaft. Manufacture date 1982. Has been suggested that since power on that is measured at base of power head would be more like 3.5 hp at prop. When compared against 6hp at prop even in a 4 stroke would this not be a significant increase in power?

Final questions. Would hanging prop on existing engine provide much change? Is there a carb kit for the old 4.5 that makes it more horesepower?

Mike

 

[pvanv]

Re: Tohatsu 6 long shaft

Yes, the 6 would give you more thrust. But only once you wind it out. So... again, you need the HT prop. I have converted a few 4's into 6's as your dealer suggested, but as Elvin mentioned, the 4 will weigh more in the end, because of the integral tank and associated gear.

You would need to contact and old-time OMC pro to see if there are any trick parts for the 4.5. Probably not, as small OB's were completely ignored by both motor and prop manufacturers until recently. But ask in the Johnson/Evinrude forum. You might get lucky.

 

[jrs_diesel]

Re: Tohatsu 6 long shaft

I have a O'Day 22, that weighs 2600 lbs. I have an '07 long shaft 6HP Mercury (Tohatsu) on the back. With my motor mount I can use a 15 or a 20 inch shaft motor. I once used a 3.5 Nissan 2 stroke, and it ran great on the boat in calm water.

My 6 came with the 7.7 x 8 prop, and while that prop works great if the motor is on my dinghy, it sucks when it's on the sailboat. The motor cannot get into it's upper RPM range. Although the motor works alright at low and midrange RPM, i know the motor will work a lot better with a less aggressive prop.

Here's an idea. That 3.5HP 2 stroke I mentioned earlier. It was made by Nissan/Tohatsu up until 2004 or 2005. It came in both 15 and 20 inch shafts, and could have either a Forward only gearset, or Forward/Neutral. The real nice thing was that it only weighs about 30 lbs, has an internal tank, and I could carry it one handed. You could grab one of those for your race days to save weight.

Now I did see where you sail you have to deal with wind, chop, and currents. In that case I would want the strongest motor I could put back there that fits the weight category. My long shaft 6HP weighs 58lbs, not counting the tank, which goes on the boat. Mine does not have the alternator or an internal tank. Rig it with the high thrust prop and that would be ideal, like pvanv said. I will likely be getting the HT prop for mine now too.