E27 prop questions

[SV_Ariel]

Can’t seem to find any info in the search bar for E27 propellers.

I have what I assume is a stock prop on my 74 E27. I have recently swapped out to a Thunderstruck EV system. I think I need a larger prop. The electric motor spins the shaft like mad but it just doesn’t seem to have any giddy up.

The boat is incredibly sluggish at initial throttle. I never ran the boat with the previous A4 so I have no frame of reference on the props performance.

At first I thought my prop had fallen off because the motor was going like mad but I barely was getting movement.

Anyway, it’s a 2 blade prop, that’s about all I know. Never measured it. I’m thinking of getting a higher torque low pitch prop, probably three blade but I don’t know what size will fit. Anyone know the diameter of the stock two blade propeller?

For years I ran a Tohatsu 6hp with the high thrust prop and it moved it really well. I thought for certain using the prop right in front of the rudder would have given me better performance.

 

[JPS27]

When I changed out my A4 for a 2qm15 initally i kept the same indigo prop that worked fine will until the A4 died. With the diesel I think i maxed out at 3 knots cruising for the short time I had it. I worked with a prop shop to get the right prop (for the engine and my circumstances). I got a 3 blade for maximum control. With many more years of experience now since that time, not sure if I'd go with a two blade. Either way, the 27's don't have much room for a larger prop in terms of diameter. I sold my boat 2 years ago and I don't remember the D and pitch (I might have some records or pics somewhere if you need that info). I do recall that the clearance was a little under recommended. And I had a lot of prop walk but also could stop the boat on a dime and spin it easily in very tight fairway. The engine was happy and moved the boat as it should.

 

[Pete the Cat]

I don't think the specs on the stock prop for an A4 is going to help. Props diameter is generally just ensuring that the tips clear the hull by an inch and a half or two (mostly for noise and a bit for cavitation). My prop friends say want to swing the largest diameter you can, and adjust the pitch to torque, load and RPM. Pitch is dependent as much on the actual torque and rpm of the motor. I am unsure how your electric motor's torque and RPM curve would compare to an A4, but I would assume it would be quite different. I have seen this problem in a couple folks who went electric and believe someone might have solved it. I used David Gerrs "Propellor Handbook" but lent and lost it, but I am not sure it would help with electric torque specs. Big help, huh?

 

[SV_Ariel]

Can’t seem to find any info in the search bar for E27 propellers.

I have what I assume is a stock prop on my 74 E27. I have recently swapped out to a Thunderstruck EV system. I think I need a larger prop. The electric motor spins the shaft like mad but it just doesn’t seem to have any giddy up.

The boat is incredibly sluggish at initial throttle. I never ran the boat with the previous A4 so I have no frame of reference on the props performance.

At first I thought my prop had fallen off because the motor was going like mad but I barely was getting movement.

Anyway, it’s a 2 blade prop, that’s about all I know. Never measured it. I’m thinking of getting a higher torque low pitch prop, probably three blade but I don’t know what size will fit. Anyone know the diameter of the stock two blade propeller?

For years I ran a Tohatsu 6hp with the high thrust prop and it moved it really well. I thought for certain using the prop right in front of the rudder would have given me better performance.

When I changed out my A4 for a 2qm15 initally i kept the same indigo prop that worked fine will until the A4 died. With the diesel I think i maxed out at 3 knots cruising for the short time I had it. I worked with a prop shop to get the right prop (for the engine and my circumstances). I got a 3 blade for maximum control. With many more years of experience now since that time, not sure if I'd go with a two blade. Either way, the 27's don't have much room for a larger prop in terms of diameter. I sold my boat 2 years ago and I don't remember the D and pitch (I might have some records or pics somewhere if you need that info). I do recall that the clearance was a little under recommended. And I had a lot of prop walk but also could stop the boat on a dime and spin it easily in very tight fairway. The engine was happy and moved the boat as it should.

Do you remember what kind of 3 blade you got? I don’t necessarily know if I need a bigger prop but I’m almost certain it needs to have more blades. I don’t think my 2 blade has enough surface area in the water.

 

[Pete the Cat]

Do you remember what kind of 3 blade you got? I don’t necessarily know if I need a bigger prop but I’m almost certain it needs to have more blades. I don’t think my 2 blade has enough surface area in the water.

I think the pitch of the blades is much more important than how many blades you have. A three blade may have less vibration but will induce more drag. But whatever you have the pitch needs to match the torque and RPM of your motor.

 

[SV_Ariel]

On the Thunderstruck website they have a prop calculator. Enter in all your information and it spits out a desired prop diameter and pitch. These were the results.

2 blade dia. 11.3 pitch 6.0
3 blade dia. 10.8 pitch 5.9
4 blade dia. 10.2 pitch 5.8

But again, without knowing what comes on the Ericsons from the factory I’m just guessing. I’d love to go buy an 11 in. 3 blade prop with a 6 pitch and slap her on there but I don’t know if it will fit.

I might have to just bite the bullet and pull it out to measure it. Thanks all anyway for the help.

 

[cptnkayak]

Can’t seem to find any info in the search bar for E27 propellers.

I have what I assume is a stock prop on my 74 E27. I have recently swapped out to a Thunderstruck EV system. I think I need a larger prop. The electric motor spins the shaft like mad but it just doesn’t seem to have any giddy up.

The boat is incredibly sluggish at initial throttle. I never ran the boat with the previous A4 so I have no frame of reference on the props performance.

At first I thought my prop had fallen off because the motor was going like mad but I barely was getting movement.

Anyway, it’s a 2 blade prop, that’s about all I know. Never measured it. I’m thinking of getting a higher torque low pitch prop, probably three blade but I don’t know what size will fit. Anyone know the diameter of the stock two blade propeller?

For years I ran a Tohatsu 6hp with the high thrust prop and it moved it really well. I thought for certain using the prop right in front of the rudder would have given me better performance.

Can’t seem to find any info in the search bar for E27 propellers.

I have what I assume is a stock prop on my 74 E27. I have recently swapped out to a Thunderstruck EV system. I think I need a larger prop. The electric motor spins the shaft like mad but it just doesn’t seem to have any giddy up.

The boat is incredibly sluggish at initial throttle. I never ran the boat with the previous A4 so I have no frame of reference on the props performance.

At first I thought my prop had fallen off because the motor was going like mad but I barely was getting movement.

Anyway, it’s a 2 blade prop, that’s about all I know. Never measured it. I’m thinking of getting a higher torque low pitch prop, probably three blade but I don’t know what size will fit. Anyone know the diameter of the stock two blade propeller?

For years I ran a Tohatsu 6hp with the high thrust prop and it moved it really well. I thought for certain using the prop right in front of the rudder would have given me better performance.

I also have a E27, hull #515. Although the serial # indicates a 74 hull, the title claims the boat is a 1975, which would make sense, as the hull is cast long before a sale is completed. Purchased the boat used. According to Ericson, the first or only one to leave the factory equipped with a diesel (Westerbeke/Buke Pilot 10). Based upon the number of installation errors committed, and the total lack of research they did related to a diesel installation, I can believe it was the first. The installation was handled exactly as if they were installing an Atomic 4, including the propeller.

The boat came with a two blade 6/12 prop, which was proper for the A4. Although the boat maneuvered well at low speed with that prop, in a strong head current, I could barely make headway. Researching with a propeller manufacturer, it was determined the boat should have a 10/12. Although there is room to fit a 13" prop, they claimed it would suffer performance issues from the tip being too close to the hull. The 10 pitch prop made a huge difference with the diesel. Although I rarely operated under power, let alone full power, the boat can now move at over 6K when needed.

I still have that bronze two blade 6/12 prop and would be happy to let it find a new home. I would consult a reputable manufacturer and given the RPM, HP, Torque of your new engine, let them recommend a proper prop.
Best wishes for success!!

 

[acubria]

My E26-2 which is kind of identical in design to the E27 and with a 1GM Diesel has a prop that says: 12RH10 . I am pretty sure it is the original prop. I am the 3rd owner. see photo.
The boat moves at about 5k comfortably. Against wind and current, you barely move.

 

[Mark F]

Hi Andrew,
(Just seeing this) EP prop size requirement is totally different than your A4. I think I have a blog here on the forum about my hit and miss approach to getting a good prop for my 6 KW electric motor setup. I have a 3 blade fixed 13x13 (right or left your choice ;-) currently. It works well but an 11 or 12 pitch might be a bit better for top speed. Again, my scientific approach is hit and miss. I think the 13" pitch prop is a bit over-propped for power but I believe I get better regen with it. Your performance is also affected by the programing of your controller... With my setup I get about 6 knots top speed (flat water and draining the battery quickly) at a 20 amp (@50volts) draw I get 4 knots of boat speed (flat water) and can motor for a long time.

 

[Mark F]

Here is the blog link https://ericsonyachts.org/ie/ubs/blog/electric-repower-of-lotus-flower-a-1976-ericson-27.773/
According to the blog I have a 13x12 prop...

 

[SV_Ariel]

Thanks for the help everyone. I had somewhat given up hope and just looked and saw a bunch of people had replied. I talked to the folks at Thunderstruck and they recommend I gear the prop down. The motor is programmed to spin at a max RPM of 2700. I’m currently running a 1.8:1 ratio. They recommend a 2:1 minimum to start and then tweak from there. I’ve got a couple different gears to change out with a max of 2.5:1. I’ll update everyone with my results. Probably should post some pics when I’m done as well.

 

[SV_Ariel]

The new boat name. My wife hates it.

 

[SV_Ariel]

If I’m supposed to post these somewhere else let me know

 

[SV_Ariel]

Custom made motor mount

 

[SV_Ariel]

Rear