Marine Hydrofoils, as manufactured by Boeing Marine Systems , have 15-5 PH stainless steel struts and foils extending below and galvanically isolated from their aluminum hulls. Both the hull and the foil system require cathodic protection. Special shaped aluminum-zinc—indium anodes with high surface area and low weight are hull mounted to cathodically protect the aluminum hull and stainless steel strut and foil assemblies. Passive control of stainless steel corrosion potential is maintained due to the current and voltage drop characteristic of low voltage drop diodes connecting aluminum hull anodes to the stainless steel. Thus, the aluminum anodes cathodically protect the stainless steel foil assemblies at approximately 300 mV more noble than the hull mounted aluminum anodes. This allows the hull mounted aluminum anodes to cathodically protect the aluminum and stainless steel at two different corrosion potentials while preventing cathodic overprotection of stainless steel. This avoids the possible hydrogen uptake into the metal that can result in reduced fatigue life when aluminum anodes are used directly on stainless steel.

Subject
Voltage drops, Foil, Steel surfaces, Cathodic protection, Aluminum, Cathodic current, Anode surfaces, Seawater, Hull, Aluminum anodes, Stainless steel, Corrosion potential, Anodes
© 1987 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1987
Association for Materials Protection and Performance (AMPP)
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