Note 2 - Summary of Significant Accounting Policies (Tables)

3 Months Ended

Jul. 31, 2017

Notes Tables

Schedule of Cash and Cash Equivalents [Table Text Block]

	July 31, 2017		April 30, 2017
	(in thousands)
Checking and savings accounts	$	4,400	$	4,241
Overnight repurchase account		7,014		4,180
	$	11,414	$	8,421

Restrictions on Cash and Cash Equivalents [Table Text Block]

	July 31, 2017		April 30, 2017
	(in thousands)
Barclay's Bank Agreement	$	361	$	334
Santander Bank		154		154
	$	515	$	488

Schedule of Cash, Cash Equivalents, and Restricted Cash [Table Text Block]

	July 31, 2017		April 30, 2017
	(in thousands)
Cash and cash equivalents	$	11,414	$	8,421
Restricted cash- short term		361		334
Restricted cash- long term		154		154
	$	11,929	$	8,909

Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]

	Three months ended July 31,
Customer	2017			2016
Mitsui Engineering & Shipbuilding		67	%		100	%
U.S. Department of Defense Office of  Naval Research		33	%		-
		100	%		100	%

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Three months ended July 31,
	2017		2016
	(in thousands)
Product development	$	13	$	53
Selling, general and administratvie		78		165
Total share-based compensation expense	$	91	$	218