See if you can borrow a 5 hp Mariner to see how it goes. I think the 5hps are standard with an integrated fuel tank and a change cock and fuel pump to accommodate an external fuel tank.
I had a 4hp Mariner on the back of a Windrush Wildfire (23 ft monohull trailer sailer about 950kg) and it worked very well pushing it along at 7 kts easily.
Two problems I had with that one was the prop pitch and leg length. With the standard coarse prop pitch the motor was not able to reach it's best RPM. With a finer pitch it would have reached proper operating RPM without losing any speed and enable the yacht to punch a swell a bit better.
The problem of course with the short shaft was that if the yacht hobby horsed in a swell at all, the prop would come out of the water and rev it's tits off and had trouble picking up the cooling water suction again.
Those little Mariners might be called the "new Seagull out board". They are a very simple single cylinder engine and if I recall correctly are very easy to start with a knotted rope if the recoil starter fails, which they rarely do.
It might be pushing it's capabilities on a Van De Stadt 32 but those boats slide through the water quite easily with a clean bum.
The Mariner 4s and 5s are so good that they are rarely sold secondhand. They are light enough that you can take them off the back of your yacht and use it on the back of your tender. If you had a Zodiac 2.4 it would be an ideal combination of yacht, tender and outboard.
If you can ascertain that the Mariner 5 is capable enough, buy one new. It will probably cost around $1400 but will be worth it. You will have no problem reselling it.
Is this the boat here
http://www.boatpoint.com.au/boats-for-sale/boatdetails.aspx?R=6640770 . If so I believe you have scored very well however you should describe this as a plywood boat rather than a timber or wooden boat. This boat will certainly be no slouch when it comes to sailing.
If everything with the hull and deck turns out to be quite sound and you do the necessaries to bring everything up to scratch, she will be an ideal east coast cruiser and worth hanging on to for a few years. If you maintain her well I think you could quite easily sell her for $15-20,000. Nobody builds these boats any more.
Congratulations and Happy Sailing.



If that is the boat I am really quite envious.

What do you reckon Multihull1????