There are many views on how best to support a boat on a trailer. Many people are emotive about it, and many are simply pragmatic!
Trailer manufacturers are tasked with providing a balance between being hull-friendly while also achieving convenient boating.
All hulls float by displacing enough water to equal the weight of the boat. As a result, hulls need strategically placed strengthening to resist cracking under pressure from the water, and this is coupled with profiling to achieve the intended type of boating required (eg sea or river use, slow cruising or fast racing, etc).
Setting up a hull-friendly trailer requires careful positioning of sufficient supports to distribute the carried weight of the boat without damaging or piercing the hull. If you rest a boat’s hull on a hard ball the hull will be punctured. If you rest the same part of a hull on a plank of wood, it’s unlikely that damage will occur. But if you increase the number of balls to (say) 20, then its likely that his will provide the same level of damage-free support as 1 plank of wood!
But clearly the balls would be the easier option for getting the boat on and off the trailer.
But materials technology has presented us with flat surfaces with superb sliding characteristics and are friendly to a range of alloy and fibreglass hulls. This has closed gap between planks and hard balls – or rather keel slides and rollers – and now the simplicity of a competent sliding surface compares attractively to a multitude of rollers with fiddly and short-lived componentry!
In boat construction, most keels perform a similar function and most also represent the strongest part of a boat’s hull. The keel is so much stronger than a section of hull that this presents as an obvious part of the boat to use for carrying most of the boat weight
Using rollers for support
Rollers are historically associated with good rolling characteristics and are popular for launching and retrieving. But their point loading is unattractive and to avoid damage there should therefore
be plenty of them. As they age and shafts become pitted, their rolling resistance increases dramatically under load, and performance drops off quickly.
Bunks (or slides) provide a high contact area and low point load contact. More expensive materials such as HDPE provide excellent sliding characteristics, a surface that is softer than gelcoat, and perform well with alloy. People do have concerns that sliding friction of bunks will damage and wear the boat’s contact surface – and this can occur when overloading and using older and harder materials still used on many trailers by unsuspecting boaties, or where keels and hulls are in poor condition.
The configuration of choice among our Spitfire Trailer clients for both glass and alloy boats is shown below with perhaps nearly 95% of the hull weight being taken by the keel, and the hull supported only to keep it upright. This compares with a full roller trailer (pictured) which supports all the boat weight under the hull – potentially the weakest support area.
Roller pro’s
– Good option for retrieving boats in shallow water – but make sure you have plenty of them to spread the loads
Bunk & keel slides pro’s
– Super slippery with more even load distribution and better hull support
– Lower height, lower cost, lower weight, less maintenance
Happy Boating
Trailer Tips by Spitfire Boat Trailers SA
Andrew van Ryneveld – Adelaide
