"As predicted by our captains and navigators the weather conditions have been very challenging," he said.
"There has often been little or no wind available to help push them east, but they've also encountered heavy seas and extremely cold conditions, resulting in broken equipment and items such as coffee mugs and spoons being lost overboard."
The crews' arrival in Tubuai late last week was celebrated by the local community, cultural groups and representatives from throughout French Polynesia, Mr Johnstone saying the sailors were happy to be back on land but no one wants to get off, "so that's a pretty good indication of their mood."
The people of Tubuai had been amazing: "Their generosity and support for our crew and for the kaupapa has been humbling. It's rewarding to see how initiatives like Waka Tapu galvanise communities and bring geographically-distant relations together to celebrate our shared heritage."
Everyone was in good health and had been enjoying the experience. The fishing had been excellent, and four birthdays had been celebrated.
Pods of humpback whales and grey nurse sharks had been seen, and the two waka had passed within ten miles of the 189-metre container ship Acquilla, but apart from that the journey had been a solitary one.
The Waka Tapu expedition had so far covered 2200 nautical miles, and the crews were resting for a few days before setting sail for Mangareva Island.
That would take another two weeks, depending on the weather.
The waka are due to reach Rapanui in late October or November.
Their progress can be followed on www.wakatapu.com