You most probably won't be able to ship them as checked-in baggage, even as oversized baggage, but will instead need to ship them as cargo, either directly with the airline, or using a carrier such as UPS.

A couple examples:

- [British Airways](http://www.britishairways.com/en-gb/information/baggage-essentials/checked-baggage-allowances) states:

> ### Oversized bags
>
> [...]
> 
> Any items **larger than 190cm** x 75cm x 65cm (75in x 29.5in x 25.5in)
> require separate shipping as cargo.
> 
> [How to ship bulky items as cargo](https://www.iagcargo.com/iagcargo/portlet/en/html/main)

- [Air New Zealand](http://www.airnewzealand.com/oversized-items#lengthrestrictions) states:

> ### Length restrictions
> 
> The **maximum length** per piece on jet aircraft is **2 metres** however this
> may be reduced depending on the width and height of the item. Sporting
> items exceeding 2 metres but less than 2.5 metres in length may still
> be accepted and are subject to oversized item charges.
>
> [...]
>
> If you wish to travel with an
> item that exceeds the allowable package dimensions, you will need to
> consider making alternative freighting arrangements for this item.
> 
> Air New Zealand Cargo, or your local freight forwarder, can advise you
> on alternative arrangements. Applicable rates will apply and items
> sent via Air New Zealand Cargo or a local freight forwarder may not
> necessarily travel on the same aircraft as you due to space
> availability. Please remember it is important to prearrange this with
> Air New Zealand Cargo or a local freight forwarder at least 5 days in
> advance of your travel. There may be occasions when Air New Zealand
> Cargo is unable to assist you with the carriage of your oversized item
> due to limited cargo space availability to your destination.

Items this length may simply not fit in aircraft holds, or be impossible to load/unload due to the relatively small cargo doors on passenger aircraft.

I recommend you:

- contact your supplier, which must have experience shipping the boats internationally, and should have good advice
- contact the event organisers, who should have experience as well with this, and may have specific deals with carriers.