New Outboarder for my 1965 Eurocraft Mars

[terano]

I would like to repower my 1965 Eurocraft Mars which is currently motorized with a 1978 Johnson 70 hp. The engine is pushing my boat to only 28 mph. The boat has no maximal engine rating (because of its age). Lenth 16', beam 6', weight 926 lbs
I am looking to the Yamaha F70, the Suzuki DF80 and the Evinrude 75.


My favorite would be the evinrude, but there is no dealer nearby. The next one is 3hours away. The Suzuki dealer is great but the engine is very heavy 361 lbs and 1.5ccm. The Yamaha dealer is good and the engine only 286 lbs and 1000ccm.
What is the impact of the weight and the strong torque of the Suzuki to my boat and the behavior?
At the moment I would like to go with the Suzuki, but I am not sure about the influenze of the weight of the outboarder to my boat.



thanks for your help

 

[Frank Acampora]

Re: New Outboarder for my 1965 Eurocraft Mars

Here is a 15 footer with a similar shaped transom that is rated for 90 horsepower. It appears to be a little narrower at the transom ( 66 inches--just under 2 meters) than your boat and currently has a 105 on the back weighing about 275 pounds. It is about 1.6 liters and swings a 13 inch prop. Torque is no problem.

If you look at the shape of the transom on your boat, you will see a reduced running surface on plane while there is plenty of reserve while sitting. At 16 feet long, if the transom is 20 inch in height, the boat should be good for up around 110 horsepower. If a 15 inch transom, reduce some--maybe 90.

You may notice a bit more torque steer with a beefier engine but nothing wild enough to put the hull on its side and nothing you can't control. Extra weight--yeah when you slow down, a following sea may break over the transom and if you have fuel tanks in the back and stand there, water may enter the drain hole in the splashwell, but I highly doubt that you will come close to swamping the boat. At over 300 pounds the Suzy is heavy but eliminating two six gallon tanks from the stern would compensate. However, it appears that there is a fill at the bow which leads me to believe that there is a tank there.

 

[Frank Acampora]

Re: New Outboarder for my 1965 Eurocraft Mars

Here is a 15 footer with a similar shaped transom that is rated for 90 horsepower.

If you look at the shape of the transom on your boat, you will see a reduced running surface on plane while there is plenty of reserve while sitting. At 16 feet long, if the transom is 20 inch in height, the boat should be good for up arouns 110 horsepower. If a 15 inch transom, reduce some--maybe 90.

You may notice a bit more torque steer with a beefier engine but nothing wild enough to put the hull on its side and nothing you can't control. Extra weight--yeah when you slow down, a following sea may break over the transom and if you have fuel tanks in the back and stand there, water may enter the drain hole in the splashwell, but I highly doubt that you will come close to swamping the boat.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

Thanks Frank
You are right the 12 gallon tank is in the front of the boat. I was simulating last weekend the weight with 5x165 lbs (5x75 kg) in the boat and 1x65 lbs) 1x75 kg in on the transom. The back of the passengerroom was still 37 cm over the waterline.
So it should not be floated. The transom height is 20 inch.

 

[RotaryRacer]

Re: New Outboarder for my 1965 Eurocraft Mars

I'd be a little concerned that if you buy a new engine of the same basic power rating that you won't end up any faster.

Is that Johnson running good? Is it making full power? A 70 hp motor is a 70 hp motor. If you buy a brand new Suzuki 80 HP motor that weighs 360 lbs vs. you current 70 hp motor at 230 lbs., you very likely could end up with a slower top speed.

I can't tell from your pictures, does your current motor have power trim/tilt?

 

[Home Cookin']

Re: New Outboarder for my 1965 Eurocraft Mars

I'm with rotary; you aren't changing anything by changing brands other than weight. 70 should be plenty and should be faster than 28 mph.

In addition to the trim, evaluate your prop. The 70 is typically rigged on a bigger boat so it may have the prop still on it for a different rig.

Cool boat, though.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

That is a good question, maybbe is the Johnson still Ok but misconfigured. There is no power Trim and I timmed to the second last slot. Maybee one or two higher Slots could help. I have currently a
13.25x17 Propeller and the acceleration is great so maybee on other Propeller with a higer number could help.

 

[RotaryRacer]

Re: New Outboarder for my 1965 Eurocraft Mars

Do you have a tachometer to see what RPMs the motor is running? What RPMs do you get when running at your top speed of 28 MPH?

Can you check the compression on the motor?

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

Here is aslo a Video on the lake of Zurich, the Sound of the engine sounds healthy :
00057 - YouTube

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

no unfortunately do I not have a tachometer to check the rpm's on my boat.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

It may also be that this formfactor of the boat Needs a lot of power. I saw a very similar boat in an old catalog. It was reated with 100 HP max .

 

[Silvertip]

Re: New Outboarder for my 1965 Eurocraft Mars

When trying to determine why you boat doesn't perform, there are several factors to consider: 1) Is the engine in a good state of tune and making full power. 2) What is the current "observed" wide open throttle rpm with what you consider an average load. 3) What prop (diameter, pitch, aluminum, stainless steel, three blade, style and condition) is installed . Every engine manufacturer specifies a recommended wide open throttle rpm range for their engines. Since the manufacturer has no idea what size and style of boat the engine will be installed on, they don't even ship larger engines with a prop. The installing dealer does that. A work boat, pontoon, fast hull, and cruisers all take a different prop when using the same engine. So you need a tach to determine what the current rpm is. That is compared with the manufacturers recommendation (about 5000 - 5500 for your engine). If your engine is only reaching 4500 rpm for example, the engine is being lugged which is like trying to climb a steep hill with your stick shift car in high gear. You correct that by changing to a lower pitch prop. For every inch of pitch change down, engine rpm rises by about 200 RPM. Conversely if the engine is reving hgiher than 5500 you would need to increase pitch to bring rpm back down to the recommended range to avoid over reving. All of this is of course dependent on the boat not being full of water soaked foam and an engine that is running properly. But without a tach, you should not even think about spending money on a prop. I also think buying a new engine with no benefit other than some fuel saving is a bad decision.

 

[steelespike]

Re: New Outboarder for my 1965 Eurocraft Mars

delete

 

[steelespike]

Re: New Outboarder for my 1965 Eurocraft Mars

To do this right you do need a tach and a gps.Some sells have an app.
The hydro foil is probably holding you back. An induction tach like the Tinytach will work
on almost any kind of motor. An optical tach would work though very hard to use on a moving boat.
Be sure your throttle is opening all the way.Motor in excellent t tune?Prop in excellent condition.
If the motor has a 2.42 gear ratio Guessing the slip at 10% that works out to about 4,700 at 28 MPH, too low.

 

[steelespike]

Re: New Outboarder for my 1965 Eurocraft Mars

To do this right you do need a tach and a gps.Some sells have an app.
The hydro foil is probably holding you back. An induction tach like the Tinytach will work
on almost any kind of motor. An optical tach would work though very hard to use on a moving boat.
Be sure your throttle is opening all the way.Motor in excellent t tune?Prop in excellent condition.
If the motor is a long shaft it has a 2.42 gear ratio Guessing the slip at 10% that works out to about 4,700 at 28 MPH, too low.
If its a short shaft 1.85 ratio it works out to 3,575 rpm very low.Of course this isn't a good way to figure rpm.
With some luck if the motor is reasonably healthy you should be able to run about 35 lightly loaded.

 

[trendsetter240]

Re: New Outboarder for my 1965 Eurocraft Mars

Don't forget that outboard HP is rated at the crank not the prop shaft so it's really equivalent to a 60hp from mid-eighties and later.

I think you would like a nice improvement with a rebuilt mid-nineties Evinrude 70hp with power trim (237lbs). If you really want to fly a mid-nineties 60 degree V4 90-115 would make that boat a rocket and weigh only 300lbs.

 

[Frank Acampora]

Re: New Outboarder for my 1965 Eurocraft Mars

If you compare your hull with My shorter and lighter hull in the above photos, you will see that the 28 MPH you are topping out at is about correct.

Here are the numbers: The 15 foot hull is a deep vee and is about 700 pounds advertised weight. With a 55 on the back it topped out at 27 MPH. In the last photo, with a 75 HP engine, it only topped out at 37 MPH.

Given that your hull is longer, wider, and heavier, 28 MPH with a 70 would appear correct.

Now back to my hull: with a 90 on the back (it is rated for 90) It will top out at 45 MPH with me alone and two tanks of gasoline.

. I suggest strongly that your Johnson (the engine that is) is working well. You 16 foot hull should be rated for somewhere around 110-120 HP. Log onto the US Coast guard site and use their formula to find the approximate horsepower your boat can handle. IF you have a similar agency in your country (Switzerland?) with similar formulae use them. If you want more speed, power the boat with between 90 and 110 HP, no less.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

Thanks for all your comments! I really think that the power of my Johnson is not 70 HP anymore maybee around 50.
Unfortunately is the Swiss Lake Guard very strict. From 2017 on are two strokes not allowed anymore on all boats (only E-TEC's). They also rated my Boat with a max of 80 hp. That means I could either invest in my 35 years old Johnson to try to make it faster or buy a Suzuki DF 80 or a Yamaha F70.
I found a great dealer with a good offer for the Suzuki but I am not sure if it is not to heavy.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

I finally bought the Yamaha F70. Today was the first test drive.
The characteristic of the engine compared with the 35 years old Johnson is really an Evolution. I'm really happy with the engine.

With the propeller we have to make further test, this because I am not so satisfied with the speed of the engine.
The F70 can theoretical go up to 6300th

Now is the standard 13 1/4 x 17 propellers mounted.
Alone at 5800 about 38 mph
with 2 persons at 5600 approx 36 mph
with 3 persons at 5300 approximately 33 mph

Next Monday, I will try a 13 1/2 x 15 propeller
I hope to come to over 6100.

 

[terano]

Re: New Outboarder for my 1965 Eurocraft Mars

Has anyone some recommendations for a stainless steel Propeller ?

Maybee a Stiletto 15 pitch?
Is there an advantage between Yamaha ALU prop 15" and Stiletto 15"?

The F70 may turn until 6300.
I made now some test with the Yamaha 17" and 15" Propeller.

13 1/4 x 17" motor speed mph km/h
1Pers 5800 38 61
2Pers 5600 36 58
3Pers 5300 33 55


Much better Response and acceleration.
13 1/2 x 15" motor speed mph km/h
1Pers 6000 35 56
2Pers 5800 34 55
3Pers 5600 33 52

Thanks for your feedback