Aventura’s Logs

Aventura IV: An unpainted tin can for all seasons

The first report on the plans for my new boat has generated much interest, and I had several questions. I’ll deal with the most frequently asked ones first.

Why  aluminium?

The first Aventura  was a strong well built GRP boat which survived a three hour grounding on a  reef on the Caicos Bank with only superficial scratches. She served me  perfectly well during my first circumnavigation but for my next boat I decided  to go for steel mainly because, once again, I was planning to explore out of  the way places and believed that a metal boat was better suited for such a purpose.

It didn’t take me long to realise that while metal was  indeed a good choice, the maintenance of a steel hull was a real nightmare and that I should have listened to my friend Erick Bouteleux and go for aluminium,  as he had done himself.

So when the time came for No. 3, the decision had already  been taken. In the following 13 years my aluminium OVNI 43 took me all over  the world, including Antarctica and Alaska, and I became totally converted to  this wonderful material.

Aventura III, my aluminium OVNI 43 took me all over the world

One of the greatest advantages of aluminium over any other  boat building material is that aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation. Aluminium oxide is  impermeable and, unlike the oxide layers on many other metals, it adheres  strongly to the parent metal. If damaged, this oxide layer repairs itself  immediately.

I must point out that my hull, and any other hull, is not made of  pure aluminium, but an alloy. Those used in boat construction contain magnesium,  such alloys having excellent durability in sea water.

Why an unpainted hull?

As on my previous boat, my main priority  was not only a strong boat but also a functional one, and, in my view, nothing  can be more functional and maintenance free than an unpainted hull.

While in Antarctica, colliding with bits of ice was practically unavoidable

One of the  great advantages of an unpainted aluminium hull, especially for those of us who  do not buy a boat to sit in a marina but to be out there sailing, is that you  can forget about gleaming topsides. As most owners will surely agree, they can  be such a worry when confronted with rough docks, barnacle covered pilings, or being  boarded by uncaring officials who often come alongside banging into your hull with  their launch without any fenders.

While in Antarctica, colliding with bits of  ice was practically unavoidable, and we ended up without any scratches to speak  of whereas friends of ours on two fibreglass boats fared much worse.

Why centreboard?

One of the first questions everyone asks me  is how safe it is to sail on a boat without a keel.

Having sailed twice across  the Drake Passage to Antarctica, both times on a centreboard boat, and having  experienced on at least two occasions winds around 60 knots, with swell to  match, was a perfect opportunity to test, and put to rest, any doubts about  stability.

Thanks to an internal lead ballast of 3.5 tons and a displacement of  9 tons, my previous Aventura was as stable as any more traditionally designed cruising boat. I am sure that the  next Aventura will be no different. I  need to point out that both the previous Aventura  and her successor have an integral centreboard, which means that the board can  be fully retracted into the hull.

There are many advantages to a centreboard,  besides shallow draft. The main role of the board is to provide lift when  sailing close-hauled and reduce leeway when reaching. With the board fully down  my previous boat drew eight feet and, when sailed properly, it could point as  high, or almost as high, as most cruising boats.

What I mean by sailed properly  is that when hard on the wind sail trim is critical, a good speed must be kept  up and heeling too much must be avoided or you end up making a lot of leeway. With  a draft of ten feet with the board down, the new Aventura should perform even better.

There is a certain technique in sailing a  centreboarder efficiently, not just on the wind but off the wind as well. This  is when the centreboard becomes a true asset as it allows you to reduce the  wetted surface. Also, the ability to lift the board gradually as the apparent  wind goes past 135°, and then continue lifting it up to the point when the  board is fully retracted, is a great advantage as the risk of broaching is  virtually eliminated. The absence of a keel to act as a pivot in a potential  broaching situation means that the boat does not tend to round up when, in a  similar situation, a keeled boat would do just that. It is a feature that I  have blessed on many occasions, and that had allowed me to continue keeping the  spinnaker up longer than I would have done otherwise.

The board was normally  retracted when motoring in calm waters and the reduction in wetted surface  provided an extra 0.3 to 0.5 knots of speed.

Why do  I consider shallow draft to be so important?

Aventura III beached

In all surveys dealing with the subject of  ideal draft there was a consensus that whereas a fixed keel may be best suited  for ocean passages, when cruising having a shallow draft boat is not only ideal  for exploring places that other boats cannot reach, but also safe because it  allows you to tuck into a protected spot if needing shelter in an emergency.

Indeed, one of the main reasons for  choosing a centreboarder is to increase my cruising options, and having a boat  whose draft can be reduced instantly is a huge advantage. The fact that most  aluminium centreboard boats have a flat bottom means that with the board fully  up the boat can dry out on any beach, tidal bay or estuary. When the tide runs  out, the boat settles down comfortably, and, as the height of the stern  platform is less than three feet above the dried out surface, access aboard is  very easy with the aid of the swimming ladder. We have dried out on many  occasions, whether to put on a quick coat of antifouling between tides while  cruising the Chilean canals, or to access a shallow bay in Alaska so we could  watch grizzly bears fishing for salmon.

One other advantage of having a centreboard,  that is nothing more than an aluminium plate, is that one can use it as a  sounding board when entering an unfamiliar shallow anchorage. It is a technique  I learned from an old friend and taught me a new meaning for the term ‘sounding  board’.