Which outboards for me ?

[earthmover]

Wow, just took a look at the Schionning Waterline 1480 website. What a beautiful machine. Wonder how difficult it would be to go electric right from the start of the build?

[valhalla360]

Obviously a different boat but we swapped out the 40hp 2stroke on our Gemini for a 25hp Merc EFI and loved it.


We lost about 1/2kt on top end but we went with a low pitch work prop and for maneuvering it was better than the 40hp but still had plenty of power to keep us at cruising speed.


So I wouldn't worry too much about it not being a high thrust model as long as you can get a low pitch prop.


FYI - the 1.3 in the hull speed equation is actually another variable that changes based on the length to beam ratio. For traditional monohulls, it changes so little that people got sloppy and treated it as a constant. When the ratio gets up above 10 to 1, the hull speed increases substantially while still remaining in displacement mode.

[cacalack]

Before spending $$, make sure current 25s are operating, when run at full throttle, in the manufacturer's spec'd max rpm range. If they are not, then a change of props might solve your problem.

[Dave_S]

Originally Posted by valhalla360

Obviously a different boat but we swapped out the 40hp 2stroke on our Gemini for a 25hp Merc EFI and loved it.


We lost about 1/2kt on top end but we went with a low pitch work prop and for maneuvering it was better than the 40hp but still had plenty of power to keep us at cruising speed.


So I wouldn't worry too much about it not being a high thrust model as long as you can get a low pitch prop.


FYI - the 1.3 in the hull speed equation is actually another variable that changes based on the length to beam ratio. For traditional monohulls, it changes so little that people got sloppy and treated it as a constant. When the ratio gets up above 10 to 1, the hull speed increases substantially while still remaining in displacement mode.

Thanks

The manufacturers agents agree with you. They don't seem worried about the additional loads on the gearbox and state it will not effect warranty if we go with a non high thrust motor. Most offer the low pitch props.

[a64pilot]

I have a little Zuk and love it, but I would not discount the Honda because it's a single overhead cam and a two valve head, I would if it were a high output 12,000 RPM bike motor but outboards are usually lower RPM motors, and if Honda can make the HP and keep the weight down, that is a plus to me.

[Jim Cate]

Dave, we don't know what your future plans might be, but if distant cruising is part of them, the requirement for dealer servicing on the Hondas could be an issue. Lots of places around the Pacific where that would not be very easy... and expensive wherever you might be!

And the query about whether your current engines are in good nick, and more importantly, are correctly propped is pertainent. I'd have thought that 50 hp would be plenty for your boat if all was properly matched. And do you have the fuel capacity to feed much bigger engines?

for reference, our 43 hp will get our ~12 tonne mono up to hull speed, slightly over 9 knots, under ideal conditions.

Jim

[a64pilot]

What brand / type is best for parts and service?
Dinghy sized motor

[Dave_S]

Originally Posted by Jim Cate

Dave, we don't know what your future plans might be, but if distant cruising is part of them, the requirement for dealer servicing on the Hondas could be an issue. Lots of places around the Pacific where that would not be very easy... and expensive wherever you might be!

And the query about whether your current engines are in good nick, and more importantly, are correctly propped is pertainent. I'd have thought that 50 hp would be plenty for your boat if all was properly matched. And do you have the fuel capacity to feed much bigger engines?

for reference, our 43 hp will get our ~12 tonne mono up to hull speed, slightly over 9 knots, under ideal conditions.

Jim

Hi Jim

It's interesting you get 9kn, you might be right, maybe I am over reving. I'm fairly sure it's not under reving.

I do expect to travel so maintenance is an issue.

Regards
Dave

Originally Posted by a64pilot

What brand / type is best for parts and service?
Dinghy sized motor

Ditto. Thanks

What would be a good choice for South Pacific.

[Scout 30]

The simple test is whether you get max rpm at wide open throttle which is the target. If it goes past max rpm you need more pitch. Most people want more speed at a lower rpm so they over pitch. This is a bad idea & hard on the motor.

[Dave_S]

Update.

One engine died. 0psi compression in both cylinders, with a bore-a-scope through the plug holes showed both pistons have gauled in the bores. Also found Salt crystals in the inlet.

Accelerated decision, I went with the Honda's. Silver Service Marine - Garry, excellent service. Came up with two other guys to do a test fit with no obligations. They will be back on Tuesday to fit the other engine and commission.

I went with 2 x 40hp, the 30's are carby motors, the 40s EFI with full monitoring and alarms via Garmin Digital displays. Still saved Weight.

I chose the 8" pitch. They will exchange for free until we are happy.

Also spoke to a guy with the same boat with remote air intake and I'll seal of the engine and draw air to the cowling from the rear deck- Approved by SSM for warranty. They will allow me to service if in a remote area and still retain warranty.

Thanks everyone for your input, very helpful as always.

[44'cruisingcat]

Don't know how I missed this thread until now!


Anyway, the Honda 40's should work well for you. One of Bob Oram's old boats has a single Honda 40, been on that boat for about 12 years, and was about 5 years old when fitted. Still going well. Would be an old carburettor model though.


8 inch pitch should see you hitting around 10-11 knots flat out. Our 20's have 7 5/8" pitch and we get mid 9 s. (Gear ratios are the same)


I'd look at ventilating the engine well as much as possible. Even when not in use. Maybe a solar powered ventilator fan?

[44'cruisingcat]

Originally Posted by Scout 30

The simple test is whether you get max rpm at wide open throttle which is the target. If it goes past max rpm you need more pitch. Most people want more speed at a lower rpm so they over pitch. This is a bad idea & hard on the motor.

You don't necessarily want maximum RPM. The manufacturers will give an RPM range you should be able to reach.

For a motor with a 6000 RPM rev limit the required range might be 5000 - 5500 RPM.

[Scout 30]

I believe Yamaha is coming out with a redesigned 25 for 2017. Might be worth checking out. However, I think the bottom line is that if you're current motors are propped correctly to get max rpm with the max diameter you'll need more hp to get a significant gain in speed.

[Dave_S]

Thanks for the info, I am happy with my choice. Nothing suited 100% but for me I think these will be pretty close.

Originally Posted by 44'cruisingcat

8 inch pitch should see you hitting around 10-11 knots flat out. Our 20's have 7 5/8" pitch and we get mid 9 s. (Gear ratios are the same)

What sort of RPM at 9+kn's are you doing?

I was hoping for a better top speed, I might need to go a bit taller in the gearing. I was hoping for a fast cruise at 10kn with twin's and single engine at about 8. I'm hoping with the EFI that I'll get pretty acceptable mileage to go with it.

Originally Posted by 44'cruisingcat

I'd look at ventilating the engine well as much as possible. Even when not in use. Maybe a solar powered ventilator fan?

I will have a vent at the top of the engine bay blowing out powered with a hard wired 12Vdc fan and an air entry plumbed to the bottom of the bay. I lift the motors up above deck height with the hatches open if I leave it parked for more than a day.

[44'cruisingcat]

Originally Posted by Dave_S

What sort of RPM at 9+kn's are you doing?

Both engines up around 5500.


If you're looking to cruise around 10, I'd say you'll need more pitch on your props. When I mentioned gear ratios being the same I meant the ratios in the gearboxes. They're (the 20 and the 40) both something like 2.08:1.