Yet another thread regarding outboard sizing

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CPseudonym

CPseudonym

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Dec 15, 2011
103
Oday 20 SF Bay Area/Monterey Bay
I have searched the forum with mixed results.

I recently acquired an O'Day 20, the previous owner motored with a 6 HP OB of uncertain shaft length.(PO died) It has an adjustable stern bracket in quite good shape. I currently own a very reliable 4.5 HP Evinrude 2 stroke normal shaft. I am fairly certain from reading other threads that the 4.5 should be enough HP to push the boat.

Would it be safe to operate the boat in a lake for a maiden voyage with this engine?
Should I upgrade to a long shaft before venturing into rougher waters?
Am I silly for considering using the short shaft at all?

Thanks in advanced for guiding me along :)

~Craig
 
MrUnix

MrUnix

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Mar 24, 2010
626
Hunter 23 Gainesville, FL
Just give it a try..

CPseudonym said:
I currently own a very reliable 4.5 HP Evinrude 2 stroke normal shaft. I am fairly certain from reading other threads that the 4.5 should be enough HP to push the boat.

Would it be safe to operate the boat in a lake for a maiden voyage with this engine?
Click to expand
Throw it on there and give it a try! I think it should be more than enough, particularly for lake usage. Original Hunter 23's came with a 5hp and are quite a bit heavier than your 20. I used to use a British Seagull (approx. 3.5hp) on a Venture 21 and it worked just fine as well.

Cheers,
Brad
 
kpgraci

kpgraci

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Jun 12, 2010
936
Oday 22 Orleans Marina, NOLA
I've done some preparatory research into the subject of outboards. I've heard 4HP per 2200lbs, which seems about right, but with current, wind, and waves I personally would prefer a bit more. The importance of long shaft is in chop and with shifting loads. If I go forward while single handed the prop comes out of the water - not good.
 
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Tom J

Tom J

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Sep 30, 2008
2,308
Catalina 310 Quincy, MA
4 HP should be enough, but at some point you'll want a long shaft. I used a 4 HP on my O'Day 23 for a while, and it was sufficient, but not great. Even with the long shaft, the prop would come out of the water under certain conditions.
 
CPseudonym

CPseudonym

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Dec 15, 2011
103
Oday 20 SF Bay Area/Monterey Bay
Thank you all for the feedback.

When I go shopping for a long shaft what HP range would be recommended for an O'Day 20? What is hull speed for this particular boat? Is there a formula for calculating hull speed or HP requirements? Is the 4 HP per 2200lbs stated above by kpgraci a standard rule of thumb perhaps?

Eventually we will be getting off the lake and venturing to SF and Monterey Bay's. The strong currents and choppy conditions of SF Bay are of particular concern me. Monterey Bay appears much more forgiving.

Thanks again for the great feedback.
~Craig
 
sailingandsuch

sailingandsuch

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Oct 29, 2008
134
Montgomery 17 Dothan, Al
I agree that for your first maiden voyage that your current motor will be enough for you. All you can do is try it. HP wise you should be good unless it is a really windy day, but I wouldn't want to make a maiden voyage on any sailboat on a day with risky weather.

As for the short shaft, you are probably going to want a long shaft eventually. I bought my Montgomery 17 less than a year ago and my buddy and I took it out on it's maiden voyage with his little outboard from a aluminum jon boat. I think it was a 7 HP and it was a standard shaft.

It was a fairly calm day and motoring out before we raised our sails was fine. Then I headed up to the bow to hank on my jib sail. As I did that the motor was coming out of the water since my buddy was watching me from near the companionway. I told him to go sit on the stern and once he did everything was fine. Needless to say we had a wonderful day!

Since then, I have purchased a 5hp Mercury with a EXTRA long shaft. I think it's 25" instead of the 20", or something like that. I did so because I have heard about even long shaft outboards cavitating in large and choppy swells and I wanted to try to prevent that. I haven't taken the boat out with the new motor yet but I bet it will be excellent.

Your Oday 20 has the same displacement as my Montgomery 17 (1600lbs) according to a quick search. I did alot of research reading online trying to decide what size outboard to get for my 17 and it seemed like 4hp was the most popular. I went with 5 hp just because I plan to take the boat across the Gulf Stream to the Bahamas in a few years and I am going down to the Keys either in late January or early April.

Depending on your uses for the boat I would say go with a 4hp long shaft and you will be happy.
 
vetch

vetch

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Dec 3, 2011
111
Prout Manta 38 St. Augustine
Hull speed is about 1.34 times the square root of the length at waterline.

I use a 6 horse short shaft on my A21 and it has plenty of power. It is mounted on the port side. The biggest problem I have is it cavitating behind the rudder if I turn sharply to port.
 
CPseudonym

CPseudonym

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Dec 15, 2011
103
Oday 20 SF Bay Area/Monterey Bay
vetch said:
Hull speed is about 1.34 times the square root of the length at waterline.
Click to expand
Thank you vetch!

I plugged that into my smartphone with my 208 inch waterline length and came up with 19.32 mph:eek:

These O'Day's are fast!!!:eek:

Then I drank some coffee and plugged in the 17 foot lwl and came up with 5.524 mph...:doh: Now we're sailing again :)

~Craig
 
vetch

vetch

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Dec 3, 2011
111
Prout Manta 38 St. Augustine
We don't sail for speed.

A coworker of mine says sailing is for people who are afraid to go fast.

I tell him power boats are for people who can't sail
 
Rick Webb

Rick Webb

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Jun 2, 2004
3,396
Hunter 23.5 Fort Walton Yacht Club, Florida
Plenty of Power

The length may be an issue.

There maybe a fix for that, I bought an extension for my outboard that increased it from a 20' to a 25' shaft. The company is Bay Manufacturing they are in Milan, Ohio. Check to see if there is a kit available for yours.
 
CPseudonym

CPseudonym

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Dec 15, 2011
103
Oday 20 SF Bay Area/Monterey Bay
vetch said:
We don't sail for speed.

A coworker of mine says sailing is for people who are afraid to go fast.

I tell him power boats are for people who can't sail
Click to expand
I soon shall be doing both. Probably won't be much good at either;)
 
CPseudonym

CPseudonym

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Dec 15, 2011
103
Oday 20 SF Bay Area/Monterey Bay
Rick Webb said:
The length may be an issue.

There maybe a fix for that, I bought an extension for my outboard that increased it from a 20' to a 25' shaft. The company is Bay Manufacturing they are in Milan, Ohio. Check to see if there is a kit available for yours.
Click to expand
Thanks for that Rick! Bookmarked that web site and contacting them next week. It never occurred to me to look for an extension.
 
B

Bill2011

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Jan 22, 2012
4
macgregor 25D Mobile AL
I just recently bought a Yamaha 4 stroke long shaft 9.9 for my macgregor 25, probably a little overkill but sure is nice to motor at about 6-7 mph. when needed. This boat had a 6hp johnson but was under powered in my opinion. love the Yamaha
 
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