Yesterday saw three well-understood non-bank mortgage providers - Resimac, Columbus Capital and Liberty Financial - each launch a new residential mortgage backed securities transaction, with the major ratings agencies assigning providing their preliminary views on each deal. Resimac's Versailles Trust Series 2017-1 RMBS is backed by a collateral pool that comprises a mix of prime and nonconforming residential mortgages. This is Resimac's first New Zealand dollar-denominated RMBS issue for 2017, aiming to raise almost NZ250 million (allowing for sellers notes to be retained). S&P Global Ratings has assigned preliminary ratings to six out of the seven classes of notes being offered to institutional investors. S&P, in a presale notes, said, "credit support comprises note subordination, lenders' mortgage insurance on 6.6 per cent of the portfolio and excess spread." There is also an extraordinary expense reserve of NZ$150,000, funded at transaction close available to meet extraordinary expense, among other positives noted by S&P.The top rated A1 and A2 notes, totalling NZ$175 million and $46.875 million, respectively, were both rated AAA(sf) by S&P.S&P Global Ratings also assigned its preliminary ratings to eight classes of prime residential mortgage-backed securities from Columbus Capital, to be issued as the Triton Trust No.7 Bond Series 2017-2. The issue at launch seeks to raise A$400 million.S&P assigned its AAA(sf) ratings to five tranches of Triton Trust notes, accounting for A$386 million of the securities offered. In its pre-sale media release, the agency explained that credit support was provided through "mortgage insurance covering 65.8 per cent of the loans in the portfolio, accrued interest, and reasonable costs of enforcement, as well as note subordination for all rated notes", along with a number of measures to support liquidity within the transaction, including an extraordinary expense reserve of A$150,000, "funded from day one" by Columbus Capital Pty Ltd.Fitch Ratings has assigned expected ratings to the Liberty Series 2017-4 Trust's residential mortgage-backed floating-rate notes. The transaction will consist of up to 10 tranches of notes, with one class of euro-denominated notes under consideration. Fitch has assigned its 'AAA(EXP)sf to the top four classes of notes, totalling A$622 million (or equivalent). The other six tranches, totalling around A$79 million, were not rated by Fitch.The collateral pool consists of conforming and non-conforming residential mortgages, totalling A$700 million, originated by Liberty Financial Pty Ltd. The overall weighted-average loan to value ratio of the pool is 73.2 per cent and an average loan size of $438,597The portfolio comprises 87.9 per cent conforming and 12.1 per cent non-conforming mortgages. Investment loans represent 42.6 per cent of the pool by balance and interest-only loans represent 39.1 per cent. These are notably higher than in the previous RMBS from Liberty (the Liberty Series 2017-3 Trust included 30.0 per cent investment and 33.2 per cent interest only loans). Low documentation loans comprise 2.9 per cent of the pool.Deutsche Bank is the arranger, and also one of the joint lead managers, along with CBA, NAB and Westpac.