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Short Shaft Engine on Post-1972 13' Whaler
freeportd	#1  Posted on 07/22/11 - 7:16 AM
Member Posts: 46 Comments: 0 Joined: 09/03/10	I have a 30HP Honda short shaft (15") outboard that I'm hoping to fit to a Whaler 13. But, I really like the smirked version of the boat which is the higher transom model (except for some 1972 models that are pretty scarce). Given that the Honda short shaft typically mounts high on a "cutout" model i.e. it doesn't rest on the transom, but is elevated by picking holes that raise the engine, is it possible that the SS Honda 30 might actually put the cavitation plate at the right height for the non-cutout model? From what I've read in other posts, ideally the cavitation plate is about 1.5" above the keel. Has anyone tried this? Usually I hear the opposite, long shaft on cutout transom. This is just the opposite. Blow out on corners, adequate cooling, are of key concern, so if someone has done this, I'd like to hear from you. If not, can anyone provide the distance from the top of the transom to the keel? I can get measurements off my engine to compare. I can then determine if it would end up at the 1.5" above keel level. Edited by Tom W Clark on 07/22/11 - 7:36 AM
blacksmithdog	#2  Posted on 07/22/11 - 11:27 AM
Member Personal Page Posts: 417 Comments: 0 Joined: 06/26/06	I'll measure it when I get home.
kamie	#3  Posted on 07/22/11 - 4:35 PM
Member Personal Page Project Albums Posts: 2975 Comments: 3 Joined: 11/04/05	freeportd wrote: But, I really like the smirked version of the boat which is the higher transom model (except for some 1972 models that are pretty scarce). . they are not as rare as you think. the problem with mounting a short shaft on a hull that requires a long shaft is the powerhead sits too close to the water. Swamp that and your stuck pretty quickly.
freeportd	#4  Posted on 07/22/11 - 5:04 PM
Member Posts: 46 Comments: 0 Joined: 09/03/10	kamie, that confuses me. Why would the powerhead of a short shaft sit any closer to the water? The only difference in the Honda SS and LS is an extension section just above the cavitation plate; the powerhead on the transom mount is the same. What am I missing? Also, wouldn't the powerhead of a SS actually be closer to the water on a cutout transom?
kamie	#5  Posted on 07/22/11 - 7:03 PM
Member Personal Page Project Albums Posts: 2975 Comments: 3 Joined: 11/04/05	how do you plan to make up for the 5 inch difference, even if you want to mount engine so the prop is one and a half inches above the keel you have to come down 3 and a half inches lower than normal. maybe i'm not thinking of it correctly, but it seems to make better sense to either get an extension kit for the engine to turn the SS into a LS or get a hull that requires a SS outboard.
blacksmithdog	#6  Posted on 07/23/11 - 3:26 AM
Member Personal Page Posts: 417 Comments: 0 Joined: 06/26/06	freeportd: It's about 21". I was measuring off to the side a little, and eye balling the keel.
freeportd	#7  Posted on 07/23/11 - 5:54 AM
Member Posts: 46 Comments: 0 Joined: 09/03/10	Thanks. I'll measure the engine today. If I recall from a prior measurement, it was about 17". If so, that leaves me about 4" above the keel....
freeportd	#8  Posted on 07/23/11 - 11:52 AM
Member Posts: 46 Comments: 0 Joined: 09/03/10	Measured Honda SS - it's 17.5 inches from transom to cavitation plate. So, mounted on a non cutout whaler would leave cavitation plate about 3.5 inches above keel. I don't think that would work well - I could envision porpoising, poor cooling, blowout during cornering, etc. Maybe I'll look to trade the SS for a LS. Or perhaps I can find a lower unit. The parts to do the conversion could add up quickly, although it appears straightforward. Edited by freeportd on 07/24/11 - 5:40 AM
Tom W Clark	#9  Posted on 07/23/11 - 2:16 PM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	Remember that transom height is just that, the height of the transom, not the length along it. The old 13 footers have a transom that slopes backwards about 20 degrees. I've measured these old boats and the length along the transom from the keel to the notch is a little over 21 inches. Going back to our highschool geometry we know that a right triangle with a hypotenuse of 21.25 inches and the top angle of 20 degrees, will have an altitude of 20 inches. This is the transom height. If the Honda BF30 measures 17.5 inches from AV plate to mounting clamp (and this is the typical measurement of small 15" short shaft motors) then it leaves the AV plate about 2-1/2" above the keel. I certainly would not rule out the possibility of the this motor working on a 20" transom Sport 13, especially if a good cupped propeller were used. Its easy enough to try, mount the motor and see how it does. It will quickly become apparent if the motor ventilates or not. You don't have to worry about cooling water; the motor will loose grip l o n g before it looses cooling water.