This is an important question, to which there is not an easy general answer. Ask your boat dealer or the boat builder if the existing platform can safely carry the combined weight of the lift and your tender. In my experience, you will rarely receive a definitive answer from either of them, especially for an older boat.
A practical way to find out is to lift your boat onto a hardstand area and test the strength of the platform.
Obtain the ‘working weight’ of your tender, add this to the weight of the lift (use 80 kgs) and carefully and gradually add ballast weights to the platform. Keep looking for any signs of flexing of the transom or the brackets supporting the platform. If either become apparent, stop adding ballast immediately. You will require stronger under-platform supports and/or strengthening of the transom. It is important you ensure the cantilevered force or moment on the stern/transom is acceptable.
Strengthening of a transom by tying fiberglass, aluminum or stainless-steel gussets between it and an athwartships hull stringer is not a difficult or hugely expensive exercise. A competent boat builder or marine engineering shop can do it if required. Also, see answers to Q7 and Images 3 & 4 below.
If your swim platform is an integral part of the boat’s structure, (i.e. no brackets supporting it underneath) the question of strengthening the transom may not arise but do check with the manufacturer of your boat.
[As a precautionary measure only, Denis added stainless gussets to his Grand Banks 42 Classic. He would be happy to discuss the process with you].
IMPORTANT INFORMATION
Please ensure you read the answer to Question 5, ‘What Warranty Is Provided with PrestoMarine Lifts’.
It is your responsibility, as the purchaser of the lift, to properly and safely cradle and secure whatever dinghy, tender, jet ski, or anything else placed on and/or lifted by the lift system. MA Products AB, Sweden, the manufacturer of PrestoMarine lifts shall not be responsible for any damage or injury to your boat, tender, jet ski or anything else placed on, and/or lifted by the lift system – see details of the One Year Warranty on pages 2 and 3 of: PrestoMarine Australia Order Form 2021.