UPDATE 2-Garmin offers to buy Raymarine for 12.5 mln stg

* Makes 15 pence/share cash offer for debt-laden Raymarine

* Raymarine has had number of approaches in recent months

* Shares jump 135 pct to 14 pence

(Adds Raymarine comment)

LONDON, April 28 (Reuters) - Garmin (GRMN.O), the biggest U.S. navigation device maker, said it made a 15 pence per share cash offer for Raymarine RAY.L, valuing the debt-laden marine navigation supplier at about 12.5 million pounds ($19 million).

Britain's Raymarine, which makes autopilots, marine radar and GPS systems for leisure boats, has had a number of approaches in recent months after announcing financing problems, and had ended talks with Garmin in December.

Raymarine said on Wednesday it is in advanced discussions with a third party regarding a sale of Raymarine Holdings Ltd, representing the business operations of Raymarine and its subsidiaries, and so urged shareholders to take no action.

Raymarine's lenders agreed in March to extend facilities to the end of September, but Raymarine still relied on the banks to waive the debt covenants while it tried to solve its funding problems, which could include a sale of the company.

It said at the time it was in talks on an offer priced at about 3.6 pence a share.

Shares in London-listed Raymarine jumped 135 percent on Wednesday to close at 14 pence, the highest price since last September.

The enterprise value of Garmin's offer is 104.1 million pounds based on Raymarine's net debt at end October of 91.6 million pounds.

(Reporting by Julie Crust; editing by Paul Sandle and Elaine Hardcastle)

($1=.6549 POUND)