I'm going to answer your question in a different way. My opinion about larger HP outboard weights and tender size and weight. My opinion is based on my experience only. A 15 hp 4 stroke is heavy. If you're not removing the outboard and leaving it mounted to the tender using a Wise Davit System mounted on the swim platform. This is a considerable amount of weight hanging off the aft section swim platform of a 29' boat. Assuming you have a CL 290 Highfield, Max hp 15 hp rated Rib weighs 126 lbs . The lightest 15 hp 4 stroke weighs 94.7 lbs Tohatsu, 97 lbs Suzuki, 99lbs Mercury,110 lbs Yamaha . I don't know what the Sea wise davit system weighs but it looks well built and I would "guess" around 100 lbs total with all components. This would be 290 lbs to 326 lbs not including the fuel tank hanging on the far aft section of the swim platform. I had a A 270 Gala very similar to the Highfield. The A 270 Gala is 8'10" and weighs 112lbs. rated for 10 hp outboard. I used weaver davits much lighter the Sea Wise ( Weaver and Sea wise are not apples to apples, Sea wise is much nicer and better built), but heavier. I wanted good performance with the Rib so 9.9hp or 15 hp 2 stroke Mercury outboard was my choice because of weight. 9.9 and 15 hp 1999 Mercury 2 stroke weighs 75 lbs. I use a motor lifting davit (Garhauer marine motor lift davit) mounted in the cockpit ( I have photo's posted in my album) and store the motor on a bracket in the cockpit. I can't lift the outboard off the Rib without the assistance of the Gaehauer davit. (Back issues) My total weight of the rig is, 15 lbs for weaver davits, Garhauer davit 18lbs ,motor 75lbs, and 112 lbs for rib = 220lbs total. 75 lbs too much. I use 75 lbs as a base line because removing my 75 lbs outboard from the boat and cruising makes a big difference. This added weight 220lbs on the aft section of the boat changes the running attitude of the C26. Most noticeably in disturbed sea's. Your 29 will except the weight better then my boat( transom beam of 8' total beam midship 8'6" C26) (Transom beam close to 9'6" and midship beam 10', 2' longer LWL and 3000 pounds heavier R29S). I believe you will still notice a running attitude change. Last summer while cruising the North Channel, Lake Huron I made a poor decision to cruise when there was a high wind warning posted, W/NW wind 30 + sustained winds. The North Channel weather buoy was posting an average wave hight 1.4 meters 4.5 feet and we saw many 6' waves all following sea's, 6 hour run, 4 hours worth without any island protection. I don't plan on cruising in theses conditions but it happens and I know it will happen again. The addition weight all aft , Rib and 75 lbs motor changed the handling characteristics for the worse, increased fuel consumption, and added additional stresses on the Volvo. After this experience and a few others since having this set up I sold the Rib this winter and I'm reassessing our tender options, lighter tender and lighter outboard.
If weight is not an issue for you and a 15 hp is the route you want to go all the manufactures you mentioned build dependable outboards. If I was purchasing a new outboard 15 hp. First choice would be Yamaha ( Good dealer network very good product ) Next would be Mercury Marine ( Good product , good dealer network) Third choice would be Suzuki, ( Good reviews, dependable motors, but dealer network is marginal in many parts of the county). Honestly, the best price would be my choice between those three options. When I purchase my next new outboard 4 stroke it will be a Suzuki 4 stroke 6hp, dependable reviews, it is the lightest 6hp 4 stroke made, will be adequate to power a smaller tender and price is right.
A 15 hp on a CL 290 will be a fun tender. The A 270 Gala with the 9.9 Mercury 2 stroke pushed the RIB, 24 mph with my wife and me in the boat. We used it all the time in the harbor and river when Lake Michigan was to rough to go out on. We used the tender as our second boat at the harbor and only took it with us when we were taking trips. It was a fun tender to use on a dingy poker run. An annual event at our homeport marina. good luck in your search and purchase of your Tender outboard.
