{"product_id":"imtra-sm13021-tunnel-steel-303-x-2000-x-10-3-millimeter-sleipner","title":"Imtra SM13021 Tunnel Steel 303 x 2000 x 10.3 millimeter | Sleipner","description":"\u003cp\u003e\u003cb\u003eTunnel Selection -\u003c\/b\u003e\n\u003cbr\u003eThe \u003cb\u003ediameter\u003c\/b\u003e of the tunnel will be determined by the model of bow thruster and its propeller diameter. Tunnel diameter refers to the \u003ci\u003einternal\u003c\/i\u003e diameter of the tube.\n\n\u003cbr\u003e\u003cbr\u003eThe optimal tunnel \u003cb\u003elength\u003c\/b\u003e is between 2 and 4 times the tunnel diameter (measuring on the short [lower] side of the installed tunnel).\n\u003cbr\u003eTunnels which are too short allow the propeller to cavitate — which decreases performance and makes a lot of noise.\n\u003cbr\u003eTunnels which are too long have higher internal friction which reduces thrust. This becomes very noticable when the tunnel length exceeds 6 or 7 times the diameter of the tunnel.\n\n\u003cbr\u003e\u003cbr\u003e\u003cb\u003eTunnel Installation Tips -\u003c\/b\u003e \nThe tunnel should be placed as deep as possible so the propeller does not draw air from the surface - which will completely eliminate the thrust. Additionally, the deeper the prop, the greater the water pressure on the blades - which maximizes the efficiency of the propeller.\n\u003cbr\u003eGenerally the top of the tunnel should be a minimum of 1\/2 x the tunnel diameter below the waterline. This is an absolute minimum and we recommend that it be at least 3\/4 x tunnel diameter below the waterline. An even better distance would be 1 x tunnel diameter below the waterline.\n\u003cbr\u003eOnce you get the top of the tunnel 1 foot (30-35 cm) below the surface, other factors should be considered more important - for example, moving the thruster further forward to get better boat turning leverage.\n\n\u003cbr\u003e\u003cbr\u003e\u003cfont color=\"maroon\"\u003e\u003ca href=\"https:\/\/image.fisheriessupply.com\/f_jpg\/f_auto\/t_Legacy-750x750\/v1\/static-images\/sipTunnelInstallationGuide.pdf\" target=\"_blank\"\u003eExcellent, illustrated guide\u003c\/a\u003e for selecting and installing bow thruster tunnels. This guide also includes many worthwhile installation tips for optimizing your (expensive) bow thruster's performance.\u003c\/font\u003e\u003c\/p\u003e","brand":"Imtra","offers":[{"title":"Default Title","offer_id":52790494593324,"sku":"ITRSM13021","price":2065.45,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0800\/5317\/4572\/files\/side-power-steel-bow-thruster-tunnels-sm13021.png?v=1774472042","url":"https:\/\/www.freeportmarine.com\/fr\/products\/imtra-sm13021-tunnel-steel-303-x-2000-x-10-3-millimeter-sleipner","provider":"Freeport Marine Supply","version":"1.0","type":"link"}