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Outboard engine size for a 500kg Rigid Raider (copy of Boston Whaler 17)

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  • Outboard engine size for a 500kg Rigid Raider (copy of Boston Whaler 17)

    Hi guys,

    Just bought another project boat, an empty hull coming from the Rigid Raider Mk1, no console or anything, the plate says “MOD 5.2M Dell Quay Marina Dory 10 men max or equivalent” (will post the pic later).

    As far as I know (may be wrong) this is copycat of the Boston Whaler 17 hull that was adapted by Dell Quay for military production for MOD. Looks like this boat was built for the military use even before the RTK Marine bought the Dell Quay Marine with all the moulds. Wikipedia claims the RTK being the originator or the Rigid Raider so now it looks like this is wrong.

    My question is about the min engine size I should go for. Looking at the RTK specs the max size was 140hp and 8 persons, boat weight 800kg (empty or with engine fitted?). I saw on other websites that the weight is 500kg, not sure.

    I plan to use it as a tiller fishing boat maximising the deck space, no console or anything, taking may be 3-4 passengers max for fishing trips. What would you recommend guys?

    Thanks in advance

  • #2
    what does the data tag state is max hp?

    if it doesnt, you need to calculate the max hp based on the OB formulas which account for lenght of boat, transom height and transom width.
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

    Comment


    • #3
      Originally posted by Scott Danforth View Post
      what does the data tag state is max hp?
      No HP rating on transom tag, this is a pre-Rigid Raider which
      was officially rated 140hp.

      Comment


      • #4
        if it was rated at 140, then any motor from 75% to 100% of the 140 rating would be good

        however if it wasnt rated at 140, then you need to go off the formula

        The Rules are in 33 CFR Subpart D 183.51 - 183.53

        Outboard horsepower ratings are based on a variety of factors. These include;

        Centerline length;

        Maximum Transom width.

        Transom Height.

        Type of steering: remote or tiller.

        Hard Chine Flat Bottom or Other.

        There is a formula for computing Safe Horsepower based on various combinations of the above factors. See the table below. This only applies to a monohull boat less than 20 feet in length (6.096 meters)

        Canada uses similar formulas for computing outboard power in kilowatts. (1 HP = 0.745 KW)

        The below formulas do not apply to: sailboats, canoes, kayaks, and inflatable boats, that are designed or intended to use one or more outboard motors for propulsion. It does not apply to boats that are true multihulls. A multihull makes two or more separate footprints in the water. A pontoon boat is a multihull.

        Taken from Title 33 Code of Federal Regulations Subpart 183.53
        Outboard Horsepower Capacity
        Compute the Factor = Boat Length x transom width
        If Factor is (to the nearest integer) 0-35 36-39 40-42 43-45 46-52
        Horsepower is 3 5 7.5 10 15
        Note: For flat bottom hard chine boats, with a factor of 52 or less reduce HP one capacity increment
        If the Factor is over 52.5 and the boat has :
        Remote Steering and at least 20" Transom Height HP = (2 x Factor) -90
        No remote steering or less than 20" transom Height
        For flat bottom hard chine boats HP = (0.5 x Factor) -15
        For other boats HP = (0.8 x Factor) -25


        Example 1: Bow Rider - Length = 19' 6" Transom width = 84" remote steering and 20" transom height.

        (Length x Transom Width X 2)-90 = HP = ( 19.5 X 7.0 X 2) - 90 = 273 - 90 = 183 (136 KW)

        Horsepower = 185 (138 KW)

        Example 2: Length 12' Transom width = 46" Tiller steering and 15" transom height.

        ( Length x transom Width) = 45.96 Horsepower from table = 10 (7.5 KW)

        Horsepower is rounded to the next multiple of five.
        Transom width : is to be measured at the widest point of the transom including permanently attached parts of the boat such as rub rails.


        Click on the image for the full size
        Transom Height Boat Length
        Boat length: Length does not necessarily include such things as swim platforms. However if the swim platform is molded into the hull and contributes to the buoyancy of the boat, it is included. If you need some more information on this call the Coast Guard at 202-372-1077.

        Click on the image for the full size
        Transom Height Boat Length
        Flat Bottom Hard Chine means: The boat is flat bottom if you can lay a straight edge across it, and there is no vee or curvature. A hard chine has no curvature.
        Special Rules: For boats that meet the following qualification there is an optional test course method for determining horsepower:

        13 feet or less in length.
        Outboard Powered.
        2 or less passengers.
        Remote steering and 20 inch transom height.
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

        Comment


        • #5
          If the boat is rated for a 140 HP motor and max 8 passengers capacity and plan tiller boating frequently with max 4 passengers don't need to go to max HP rated, 50-60% of it will suffice correctly propped for 4 up. Wich is the max HP and motor brand with a tiller available these days ?

          Happy Boating


          Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

          Comment


          • #6
            I am not sure you can get a 140HP tiller model. I know the torque on my 150HP motor would make tiller steering unusable.

            My neighbor had a BW 17 footer with a 90HP motor. It worked well.

            Comment


            • #7
              Iskander,

              Do you plan buying a second hand or a new tiller motor in the 50-70 HP range ?

              Happy Boating


              Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

              Comment


              • #8
                Originally posted by Sea Rider View Post
                Iskander,

                Do you plan buying a second hand or a new tiller motor in the 50-70 HP range ?

                Happy Boating
                Mate, yesterday I bought a used Honda BF60 2010 with 400 hours on it and full history. The engine is controlled with side mount and I called Honda about a tiller. In the UK the tiller handle set up is available up to 30hp but you can separately order the tiller kit for up to 100hp.

                When I looked at my BF60 Owner Manual all the pics are with tiller handle. The cost of a new handle for this engine will be about £400 plus VAT so we are talking £500.00 final price. I think it may work well with a fishing boat set up as the center console would jeopardise too much of deck space.

                Comment


                • #9
                  Right on mate,

                  Bit expensive but it's nice to count with more available space, a central console installation is a deck space killer. You can install a tiller extender and a high cushioned rear seat with locker and boat all day long....

                  Happy Boating


                  Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

                  Comment


                  • #10
                    Originally posted by Sea Rider View Post
                    Right on mate,

                    Bit expensive but it's nice to count with more available space, a central console installation is a deck space killer. You can install a tiller extender and a high cushioned rear seat with locker and boat all day long....

                    Happy Boating
                    Sure mate, this is the set up I want, just watched on YouTube there are versions of Verado 300hp with tiller so does not make sense to me to limit the engine size in the UK

                    Comment


                    • #11
                      A friend of mine has a 14.5 footer Boston Whaler with a light center console powered with a 2 strokes Tohatsu MC40 motor correctly propped for 2 up with a tach, achieves 6K wot revs which is the max rpm factory stated.

                      Click image for larger version  Name:	BW-14.5 Ft..JPG Views:	1 Size:	98.2 KB ID:	10786691

                      The combo is scary at full hammer down, imagine yours with a 60 HP motor. Just prop it right with a tach to run around middle wot rpm range when boating with 4 up, when with 2 up motor should rev closer to its full wot rpm range.

                      If plan installing a rear high cushioned seat and locker install an induction hour/tach on tiller arm, great for recording run hours, PM periods, and prop maximization to get the max out of that nice 60 HP.

                      Click image for larger version  Name:	Extended Tiller.JPG Views:	1 Size:	167.2 KB ID:	10786692

                      Click image for larger version  Name:	Tach & Extender.JPG Views:	2 Size:	64.8 KB ID:	10786693

                      This is a reinforced, resized tiller extender for my particular boating needs, excellent to boat all day long at speed while comfy seated. A tiller extender is usually used for trolling at low speeds would recommend to decrease the swivel bracket steering load to bare minimum for a smoother tiller driving.

                      Usually larger HP motors are for central console installations on larger boats, there are some few souls that likes tiller steering....

                      Happy Boating



                      Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

                      Comment


                      • #12
                        Originally posted by Chris1956 View Post
                        I am not sure you can get a 140HP tiller model. I know the torque on my 150HP motor would make tiller steering unusable.

                        My neighbor had a BW 17 footer with a 90HP motor. It worked well.
                        ive seen mercury 250 hp tiller drives.With correct accessories you can easily operate with little to zero effort.https://www.mercurymarine.com/en/ca/...ng/big-tiller/

                        Comment


                        • #13
                          Gee, a tiller 250HP motor. Who would have thunk it.

                          With the correct trim tab and other torque-cancelling accessories, I believe you could cancel the torque at a particular trim setting. However, every motor I tried had different torque at different trim settings. Most pull right when trimmed down and less or zero as you trim.

                          For Example, my current 135HPV6 Merc with a "Torque Tab" pulls right at planing speed, then zero and then left as I trim to max. Is their some auto-torque adjustment, that can be adjusted as needed?

                          Comment


                          • #14
                            Large tiller steer motors counts with an hydraulic steering system for a smooth and effortless tillering, If a standard portable size motor tires your hand badly on a long run, imagine those monsters....

                            Happy Boating


                            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

                            Comment


                            • #15
                              Sign up today
                              First time I ever saw a big tiller boat I chased after him as best as I could till he slowed down and it was a 225hp merc! As Sea Rider stated it had hydraulic assist im sure.According to the vids ive seen the new merc system is absolutely effortless to use and zero fatigue.
                              Last edited by 82rude; August 15th, 2019, 03:37 PM.

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